I know the compression on the LT1 is higher than the L98, but how much HP difference is there between and actual Lt1 motor and an L98 with an Lt1 intake?

 

Which LT1? Some were rated at 260 HP, some at 300 HP, some at 330 HP, etc. The typical F-Body LT1 would have about the same peak torque as the L98, but more HP due to the vastly improved cam and port runner designs. The L98 cams are intended to make lower RPM power, and suffer breathing difficulties at the upper RPM end.

The true LT1 would also enjoy the advantages of the higher compression as you describe, better head / runner design, sequential injection versus batch, and individual cylinder spark timings. The reverse flow cooling not only allows more static CR, but more fuel and timing advance before detonation. The lighter PM con rods, crank, and pistons, and better overall crank balance allows more RPM and power as well.

Other than that, it's about a wash.