Early '51 Merc. overdrive Transmission

[Alaska Jim]

I am reinstalling the 3sp w/ o/d transmission in my '51 Merc. after rebuilding it. My question is how much gear oil does this transmission hold. My factory manual only shows capacities for a 3 sp . manual transmission, not the overdrive. It calls for 3 1/2 Pints. I also have a book by Randy Rundle that states it holds almost a gallon, and that "after filling both the front, and rear half's of the transmission, you will have about a pint left over." Since there are 8 pints in a gallon, that would mean that the transmission with the overdrive holds about 7 pints. this is a 3 1/2 pint difference. Do any of you know for sure what the correct amount is? when I drained out the transmission for removal, I got les than half a gallon in the drain pan. I know that you are supposed to fill each part of the transmission until the fluid comes out of the fill plug, starting with the overdrive section first, then the main transmission section. I want to make sure that I do not have to wait for a specific amount of time for the 2 levels to equal out. I want to make sure the Trans is filled correctly. I do not want to have to pull this trans out again. After 50 years of working on cars, maybe I am second guessing my self, It is not like I have never filled a manual transmission before. I am just trying to find out the correct amount of fluid. I know the recomended type is API GL1 80-90 wt. Thanks -- Jim