This old iron was build very well. However, anything that has been sitting that long could be marginal at best. It would be a lot of extra work to service and install it and then find out it had some leaks or didn't shift well. The recommended fluid for the early hydramatic transmissions was Type "A". If it is still available it would be quite pricey. I believe it crosses to a newer product in the Dexron series. It also takes about 10 quarts.
Fred


1956 3100 Pickup/Red/350/3sp OD/PS/Disc Brakes
1957 Bel Air Sport Coupe/Red/355/TH350/PS/Disc Brakes
2017 Silverado LT Single Cab SB/Black/5.3/6 Speed Trans
1947 Willys CJ2A w/F-Head engine