In the 94-96 Caprice/ Impala SS there were no 4 bolt main blocks. I not douting your block is a 4 bolt but if it is it is it is not factory. Somewhere along the line it was swaped out from the original block.
HVY SS

 

It was replaced 4/6/2000 pn#12524896 ENG-LT1GW

 

ttt is that a 4-bolt crate motor part?

 

The horsepower differences between the B-Body and F-Body LT-1s (260 vs. 275hp) are mostly in the intake ducting and exhaust. The heads are iron and there is a slight difference in cams. The B-Bodies LT-1s were engineered to produce more torque and I think they have 10-15 more lbs.-ft.

So if anything you may come out with a little extra torque.

 

Whats the HP diff have to do with whether or not it is a 4 bolt?

 

I believe that this has turned into an informational post. A little extra info never hurt anyone...