When comparing the price between earlier and later headbolt kit, you all have probably noticed a huge difference in price. About 100 dollars in some cases.

I'm trying to find out if anybody has had success drilling the two outer headbolts and tapping them for the Longer 04 and later bolts.

The issues i see are possible casting problem with the blocks, If the bolts were made shorter because if a cavity in the water jacket or something to that effect, you could actually drill the whole out too far and ruin the block.
if anybody has heard anything about this or done this themselves i would like some info.

Or if you happen to know the reason GM used the two shorter outer head bolts.