Only way your gonna get 80 hp from those mods is to include a 60 hp shot of nitrous.
ROFL...more like 75 shot!
Seriously, those underdrive pulley kits only help because of the water pump slowing down. The alternator spins almost 20,000rpm when you're winding your motor out to 5000, so I'm sure slowing it down to 18,000 isn't helping much! Now, the crank pulley makes a difference cause you're slowing down your power steering pulley, too.
I'm going to add a fluid damper harmonic balancer to mine cause I think you're better served with one of those - they're better for the engine and have been proven (I know - so have u/d pullies) on performance vehicles for years. March has an #1158 SFI certified fluid damper that has an underdrive pulley attached for ~$120.
My plan is the 1158, a bigger w/p pulley from a police CVI, a bigger p/s pulley from 3.8, and a Cobra water pump (less drag and higher output). I KNOW that setup is gonna outdo any out-of-the-box u/d pulley kit and I'm guessing maybe 20-25hp tops realistically.
The only problem I see is maybe the alternator too low at idle (it barely keeps up now). The stock alternator pulley is 2.6inches and when idling at 700rpm, it's spinning like 1820rpm (no wonder i notice the lights dimming!). If I put the u/d crank pulley / damper on it's gonna slow down to 1625rpm (YIKES). I can get a 2" pulley for the alternator which will bring it to 2100rpm, better than stock (whoohoo, we're charging now baby)!
As to the 80hp you were quoted, I'd be willing to bet if you ran electric pumps running your p/s fluid & your water, installed a fluid harmonic balancer, and just had the crank running the alternator - you might hit half that figure downhill with a tailwind!!! Are you sure he didn't say the MAF is 80mm?