What years where 460's balanced internally vs externally?
1978 & earlier are internal balance, while 1979 & up are external balance.
The balncing is done at the flexplate and the spacer/sleeve between the balancer and the timing cover; the external balance flex plate has a weight welded to it while the external balance spacer has a "hatchet weight" swinging from it. The internal balance engines have niether weights.
The internal balance crankshaft will not readily drop into an external balance (D9TE-AB casting) cylinder block.