[rotorwrench]

Chevrolet started using the T10 in 1957 on the Corvette before GM started making their own Muncie and Saginaw transmissions. They used them a lot up to mid 1963 when they started using the Muncie 4-speeds for heavy duty applications. The Saginaws were used in lighter duty use. The T10 made a come back when the super T10 came out for high horse power applications. All the bolt patterns had changed by then.

Ford started using the T10 in 1960 with very little change till 1965 but all were the cast iron case for both the small block and larger applications and had the narrow bolt pattern. The T10 was based on the T85 but was originally used by GM since they had the design patents for the 4th gear in reverse position and reverse in the tail housing. This got BW the exclusive manufacturing rights for those first years of manufacture. Ford later came out with their own top loader 4-speed that was loosely based on the T86 after the patents on it had mostly run their course.

I could find no information that gave evidence that the Ford T85 and early pre-66 Ford T10 have a different bolt pattern. GM did not use that pattern in any info I could find. Studebaker used the Ford pattern for a time. Ford's 259 series transmissions also used the same narrow pattern for interchangeability with the heavy duty T85.