3 on tree to auto swap

Any slant 904 up through 67 with a stock converter will directly bolt to your block. 68 and up 904's will physically bolt to your block but 68 and up have a larger converter snout that is too big for your crank (unless you get the crank pocket machined). Next issue is how are you going to shift it - aftermarket floor shifter or keep it a stock style column shifter, in which case best option is to use the column and associated linkages from a 66 A Body.