[rotorwrench]

The gears from a up to 50 or early 51 F1 pickup would still work less the main output shaft but they might not be a ratio a person would want. 1949 thru early 51 Mercury transmissions still used early type gears with some minor improvements but it's the same deal with the output shaft and especially if it has overdrive. 1951 was a change over to improved gear tooth design but the Ford & late 51 Mercury and up had the 1-inch 10-spline input shaft so they wouldn't be an ideal replacement. Lincoln had the close ratio gears for a long time but a person has to have a different rear axle ratio to really be able to appreciate them for highway driving.

The later 39 & up gears have to have the 91A type fork to get the positioning right and that complicates things if a person wants the original angled shift tower like the 32 thru 35 have. If they can live with the vertical tower, then it's not much of a problem. Early gearboxes may not fit the larger clusters in the case. Smaller clusters should work.

There is a lot of interchangeability with the light duty 3-speed. 78 & later pickup top shift cases will all work for a 39 type or later blocker style synchronized transmission. The ones from 40 through 48 cars are all a direct replacement including the main output shaft for car applications. You have to watch for Mercury cars. They sometimes have the 29/14 (see post #8 below) tooth ratio. I like that ratio with 3.54 rear gears on a light body car.