The later gear sets from a side shift trans will definitely go into a '39 top load case, as well as the earlier top load cases. I just put the later 29 tooth cluster/15 tooth input gears into a 35 top load case, (along with having 3.54 ring & pinion in rear) and the quality of shifting is so much better than it was with the original 35 gears, like night vs. day, and this also seems to have eliminated the jumping out of 2nd gear. However, this could be mostly due to making sure all gears, spacers, etc., had nominal to minimum clearances.
I should also note that I did not use a 39 style shift tower, with the standard/original wide fork. A friend made a presission set of special forks, where all pieces required were tig welded together, that assembled directly into the stock 35 shift tower that slants back towards the rear of the car.
