This 1970 Boss Mustang packs a 427-cubic-inch secret

Two Hagerty Drivers Club members, Doug Miller and Joseph Sprague, connected by way of a very special muscle machine. It might look like an ordinary Boss, but under this Mustang’s hood is a little 427-sized something by way of Holman-Moody—and Le Mans. When it came time for Doug to pass the car on, he made sure it landed in good hands. To join the Hagerty Drivers Club, click here.

Doug says:

That Mustang was a rocket, I tell you, a rocket. What a blast. I had the motor of my dreams and a car that was made to handle it. The thing tracked straight as a string and it was as safe as being in your bed at night. Never squirrelly, just outrageous.

Back in 1973, my buddy and I found a 1970 Boss 302 Mustang on a used-car lot in our town of Midland, Michigan. It didn’t sound very good when we started it up, and it read zero oil pressure. So before buying the Mustang, we took it to the Lincoln-Mercury dealer across town where we worked, ran it up on the hoist, and dropped the oil pan to check the internals. The oil pump drive was twisted in half, and there were lots of tiny aluminum pieces in the pan. We gathered the metallic bits up in a nice oily shop rag, went back over to the used-car lot, and dropped them on the salesman’s desk. “Let’s deal,” I said.

Right after I bought the Mustang, my buddy and I pulled the 302. We rebuilt the motor, dropped it back in the car, and I drove it for the next year. That 302 was great for racing streetlight to streetlight, but I wanted to go faster. I had always dreamed of owning a 427 Cobra, from the time I read about one achieving something like 0-to-100-to-0 in like 10 seconds. Well, in summer 1974, a local guy named Mike had this Shelby Mustang with a 427-cubic-inch V-8 in it. All the gearheads around town thought it was a 427 “Cammer” engine. I knew better. This mystery motor was Ford’s 427 FE overhead valve V-8, like the one used in GT40 race cars. The exhaust tube on the third cylinder, each side, crossed under the engine and over to the other collector. It made such a unique exhaust note.

Well, the 427 had started to make a little rattle or something, and Mike decided he didn’t want to mess with it anymore. He was tight with his money, and it was going to cost him big to send it down to Holman-Moody for a rebuild. Instead, Mike decided he wanted to trade the engine for something less radical. We ended up making this convoluted engine swap between three cars—nothing short of a backyard mechanical miracle. In the end, Mike ended up with a K-code 289 in his Shelby, and I had a 427 big-block, the motor of my dreams, in my Boss Mustang.

I still remember the way I was shaking from excitement the day I dropped the 427 into my Boss. Since those ’70s Mustangs could be ordered with a Cobra Jet engine, the engine bay configuration and all of the motor mount locations were ready to handle a big-block.

Midland was a Chevy town back then, and nobody knew what I had. I’d pop the hood, tell them it was the Boss 302, and they’d stare at that big motor, having no clue that it wasn’t. I kid you not. I had so much fun with this car. I think back to my time street racing on Monroe Road, 2 miles out of town. There were a lot of fast cars racing out there—396 Chevelles, 396 Camaros, plenty of pretty fast small-block cars, too. Whenever I’d race my Mustang, I’d let the other guys pull away a little, and then right at the end, I’d zoom right past them. Just nose them out. They’d say stuff like, “Man, that was a great race!” I’d nod and agree, knowing I was sand-bagging the whole time.

To this day, I think back in amazement to some of the things I did with that car. But time passes, and eventually I reached a point where I could see that the car’s future was not with me. A few years ago, I chanced upon Joe Sprague through a mutual friend. We hit it off immediately. I looked at Joe and saw a lot of myself back in the day, when I had the energy to come home from work and go right out to the garage and start wrenching on stuff. We agreed on a price for my Mustang and made the deal.

When Joe gets that thing back up and running, he’s going to have a smile so wide. No matter what I did with small-blocks, it never compared to the big 427. You’d stand on the gas, and this thing, without a hint of hesitation, would roar. I can still hear it. Before long, Joe will know that sound, too.

Joe says:

I was on the road for work, in a hotel room in Houston, and my buddy Randy called me. He told me about a 1970 Boss 302 Mustang with a non-original motor and gave me Doug’s phone number. I remember talking to Doug for the first time, and he’s like, “Well, it’s got a 427 in it, and it has the aluminum heads.” We agreed on a price, and I immediately started researching the car.

I looked up VINs and part numbers, and I interviewed people who worked on the car. It was so much fun reconstructing the car’s history and tracing the engine back to 1967. After two years, my conclusion is this: The 427 was one of 10 blocks sent to race in France at Le Mans with the 1967 GT40 J cars. The engine was unused in the race and sent back to the States. Somehow it ended up at a speed shop in California, and eventually under the hood of a 1967 Shelby GT500. The owner of the GT500 swapped the 427 for a K-code engine, and that’s how it ended up with Doug’s friend, Mike, in Midland. Even though the intake was replaced with a tri-power setup, the big motor has its original aluminum heads, Holman-Moody water pump, and aluminum crank pulley.

Sure, I own the car, but it’s Doug’s story. I still keep in contact with him. Every time I find a new tidbit of information about it, like when I got the Marti Report, I share it with him. I feel like, in a way, it’s really his car and I’m just holding on to it for him. The Mustang meant a lot to him. Anytime you sell something, you’d like to think that whoever gets it after you will appreciate it as much as you did. That’s what I’m trying to do.