Picked up a 91LX...w/mods..HP???

This car is going to feel much better than a 98 Cobra because it makes more torque and at a lower RPM range. The 5.0 will feel more violent whereas the 98 will have a smoother application of power. The 5.0 might actually be slower, but will feel faster.

As far as the combo you have, it seems to be a decent starter combo. I assume those arent the GT40X heads and by FRPP intake I assume you mean GT40 or even Cobra. Your car should be in the 250-275 rwhp range without worry. I know its a broad area, but every car, dyno and area is different.

My friend just grabbed an 88 or 89 hatch with a very similar combo. GT40 intake, GT40X heads, E cam and all the bolt ons. He says the car pulls hard and on a 125 shot went 123 mph in the 1/4!