the 4.000 can be a 454 crank it this point if you used a stock Gm 454 crank or stock replace ment crank you will have a external crank so will need a 454 damper and fly wheel . if you go after market on the 4.000 crank i think you can get one internal cut for the 6.135 stock rod . you have to look in to this i have one at the shop i was not going to use it .i have to see what the counter weigths are cut for what size rod. for moving up to the 4.000 crank should not be a very big deal 366to 427 and 396/402 all use the same stroke crank that is 3.760 or 3.765 so 240 more stroke is not much if you use a cap screw rod and not a threw bolt rod that will help with room . i am not going to say that you will not have to check it and you may want to clean it here not a big deal