Horsepower guess?

I have almost exactly the setup you're suggesting...mine is:

77 360 +.040
8:1 Federal Mogul pistons
Magnum Heads-R/T Springs and Retainers
Summit K6901 camshaft
Eddy Air Gap intake for Magnum Heads
600 Holley Vacuum Secondary
Spitfire 1 5/8" Shorty headers-2" head pipes-2.5" dynomax mufflers (don't ask why it has 2" head pipes)
Modified electronic distributor to give 14 degrees BTDC inital advance, 34 degrees total advance (I still need to quicken the rate a little)

This engine pulls 14-15 inches of vacuum as of right now with an 800rpm idle.

I put this combo into desktop dyno (not sure how good it is) but it came out with 373hp@5500rpm and 396 lb-ft @4000rpm. I had put in commonly accepted magnum head flow numbers out of Mopar Action magazine.

with a 4-speed, 3:23's, and 225/60R15 goodyears, the car does not get traction at under 20mph at WOT in 1st. You can burn them no problem. Still working on the "economy" setup on the carb, but I'm getting about 12.5 MPG.

Its not a bad combo at all. Once i get the main bearings replaced (this was a used short block), i can run a thinner than 15w-40 oil and probably pick up a little power.