My 70 429 bell housing bolts for the trans to the block and for the stand were 7/16ths by 14 thread and yes i believe it is a 5/8 head for the wrench. Depends on how long the spacers on the stand are for the length. The spacers on my stand are about 2 inches so maybe about 2 3/4 or 3 inch bolts. You can always use some washers if they are too long. There are some holes in the head that are 5/16ths but I would use the 7/16ths bell housing holes to hold that weight.