Agree with W8Dart421 on the Mallory int. vs ext. thing. It's a lot of money for not much return; all 454 BBC are external with 4" stroke and about the same rod length. The mark-up on the stuff is about the same as gold - it's only tungsten ("Densalloy" is another one), but has to be alloyed to make it machinable so its $$$. You could do a slower but much less expensive job by substituting lead or (for those who believe in dieing young) mercury. The key to this stuff is the relative density of the "slug" material over the steel or iron it replaces. Tungsten is 147% heavier, so replacing a 1/2" cylinderical section with it adds a lot, mercury less, and lead only 43% heavier than steel.
For example, if the equivalent lead weight would have to be 75% more volume than Mallory to make up the same imbalance: if 4 slugs 1/2" X 1" were used, you'd need 7, etc. Drilling 3 extra holes to save $200?!!
From the standpoint of crank stress: yes, I would agree in theory that having the counterweights next to the imbalance (crank throws) instead of hanging on the outside is better.
Ideally, each counterweight should carry the imbalance of its rod pair (total of 8 weights), but many internally balanced motors have NO center counterweights - all the balancing is on the outer weights; Chrysler hemis only have 6 weights, which leave the weakest center area with heavily eccentric weight. They seemed to do OK?