What day? If you can swing the merc buy one, I like later trannies but depends on what was available for the time period you're shootin' at. A 40 rear will probably hold up just fine or in the pinch the A will work, or. . . Anyway it just depends on when you went to school as to what old school parts you need to buy.
you should start by getting yourself a dictionary. any 24 stud flatty and 37-40 rear is a good choice for width and strength. i also prefer the old ford ******'s cause im stubborn. the t-5's and such dont do much for me....