SBC carb selection and upgrades

[Rayson64]

I just bought a '86 Malibu Skier yesterday. It has the standard issue 350, iron exhaust with the only upgrade being a brand new Edelbrock 1409 (600 cfm) carb.
I have, sitting on the engine stand, a long rod SBC400 that I built about 10 yrs ago for a Tahiti jet boat I owned. Its got ported/polished heads, Rex Marine 4" alum exhaust, Weiland Stealth intake, 268 cam and a rebuilt Holley 650 vac secondary carb, BW 72 series tranny.
I like the idea of using the engine currently in the boat because I'll have to go to 1 1/8" prop shaft/strut/prop to handle the torque of the SBC 400. If I take the exhaust and carb off the SBC 400 and put on the stock Merc 350, would i see much of a performance gain or would I have to change out the cam also?
I'm looking for more torque for towing barefoot skiers, so i need to see some more power up in the 3800-4500 rpm range.
Thanks,
Lance

[cstraub]

Best bang for the buck would be a set of World SR Torquers with a cam change coupled with your exhaust. You should be able to get a legit 325 to 340HP out of this mill with these items. Should come under $1K budget if you are doing the wrenching.

[cfm]

What intake is on the 5.7 ? If the low rise quadrajet (4 hole top) GM cast iron intake I would replace this for a start. These start to kill power around 3800-4000rpm even on a low 260-270hp SBC.