[Bannon]

In my experience Underdrive Pulleys are worth about 6-7 hp and an K&N filter is worth about 3 hp on a 215 hp 5.0 liter.

I did these mods plus a Flowmaster cat-back exhaust and timing advance on my 95 mustang GT and pulled 192hp at the rear wheels. I never measured before hand but given the typical 15-20% driveline loss the motor should have pulled between 172-182 hp at the wheels stock.

A K&N might be worth 15 Hp on a 700 hp motor if the alternative is a stock paper filter

In my experience you need to be careful with underdrive pulleys. If your cooling system is adequate to marginal, underdrive pulleys will get you into cooling trouble fast. My Mustang ran hot in the Texas Summers after putting on the underdrives.
My point is that some cheap horsepower gains are a tradeoff... A K&N might be worth 15 Hp on a 700 hp motor if the alternative is a stock paper filter. When I visited Bob Norwoods shop in Dallas Texas several years ago I was told yep, K&N's will gain you some power but you know what, they are a crappy "Filter".

I agree with the other folks here, to some extent you've got to pay to play. Go for the heads and intake/cam combo and you should at easily exceed the HP numbers you are looking for.

Good Luck,

JB