The MGB received a new five main bearing engine in October 1964, derived from the new Austin 1800 FWD sedan. The rev counter gear was deleted and an electronic tachometer fitted. The U.S. oil cooler was standardized in other markets.

Sales continued to climb, setting a record of 26,542 units which would not be surpassed until 1977. U.S. sales increased to 16,753 units, four times the number of cars sold in the UK. The MGB was fitted with Lockheed front disc brakes from the outset and rear drums. The front suspension sub-frame was separate with rack-and-pinion steering, and insulated with rubber blocks. Armstrong lever shock absorbers were fitted at both ends with the front shocks doubling as the top A-frame in the coil and wishbone suspension. Splined 60-spoke knock-off wire wheels were optional, initially with eared caps, until safety requirements in the U.S. and Germany in 1966 replaced the caps with octagonal units.

A heater and demister were standard except for hot climates like Australia. A fender-mounted mirror was fitted and one or two driving or fog lights were optional factory accessories. A front sway bar was also optional.

Early MGBs had one of two convertible tops. The most common was the so-called pack-away top which could be dismantled and put in the trunk, enabling enough room for a child behind the front seats. Early cars had and optional cushion for the rear deck. Some cars had an attached folding convertible top which was finally standardized in the Mk II model in 1970. A top boot was included and matching tonneau cover was optional. Black, Red, Grey, Blue or White fiberglass factory hardtops were optional. Black convertible tops were introduced as an option to the colored ones this year. All convertible tops, top covers and tonneaus were black from 1967 on.