remember guys, erik is 16 and not made of money....I guess I don't see doing a piston swap without a bore job, and you're probably looking at $700+ for some KB107's, rings, getting the new pistons pressed on the rods, & bore & hone....
$175 is a very good deal if the shortblock is a good, running engine, and a fair deal if it needs to be rebuilt. I'd probably tear it down at least checking the conditions of the bearings, and maybe replacing them and the rings...
sounds like you already have the mag heads, so I'd use those. they flow a little better than stock 360 heads with smaller ports (better velocity) and smaller chambers (more compression). with the .028" thick MP or MR. gasket head gaskets and a 63ish cc mag chamber, you're looking at about 8.7-8.9:1 compression with stock 360 pistons. if you didn't have them, the stock 360 heads aren't bad, either. definitely use the GM3100 springs/retainers and the mag locks--comp doesn't have a recommendation for springs for mag heads, because they don't make any retainers for them....but the GM springs are a good generic performance spring, in the regards that they're 330-365 lb/in rate, will have 90-100lbs seat pressure at they're typical install height on a mag head (~1.6-1.62" or so), and coil bind at 1.06", so you're looking at about .480-.490 max lift, so they're very comparable to a comp 901 on an LA head.
definitely use some headers, I'd probably get the summit or flowtech ones based on price (flowtech ones are $280 ceramic coated from summit).
intake, IIRC the street dominator is a single plane, longish runners, and 318 port size. should be an OK intake, if you already have it, but a better intake for your combo would be a dual plane, I'd probably look to the stock 360 manifold (on the cheap) or an eddie performer (next cheapest, will gain you a little low end torque, but cost you a little peak HP over a stock 360 intake) or a eddie RPM/LD340/air gap (most expensive).
cam. remember, magnums use 1.6 ratio rockers, so to stay "safe" on the lift with the GM springs (without knowing the exact installed height of the springs on YOUR heads), you're looking at a cam with a lobe lift of about .303" max (ends up being .485" lift with 1.6's, or .455" lift with 1.5's.
here's the cams I'd look at:
summit k6901 cheapest, $100 for cam/lifters is 276/286 adv. dur, .441" lift with 1.5 rockers, .470 with mag rockers, 218/228 .050 dur, 114 LSA, 53 degrees overlap. with that much overlap, should give a pretty lopey idle, but the .050 duration numbers being rather tame, should give good drivability and street manners.
MP .450/.455" lift cam 268/272 adv. dur, .45/.455 lift with 1.5 rockers, .480/.485 lift with mag rockers, 228/231 .050 duration, 110 LSA 50 degrees overlap. similar idle to above cam, more .050 duration will give more peak power potential, and provide it higher in the rev range, the narrower LSA will boost some of the midrange torque loss due to the increased .050 duration. should behave very similarly to a comp XE268 in a 9:1 LA 360.
comp XE256 256/268 adv, 212/218 .050, .447/.455 lift w/1.5 rockers, .477/.485" lift with 1.6's, 42 degrees overlap. should have a near stock idle, and make very good torque. should have stronger idle-3500RPM power/torque than the above, and probably won't sacrifice much in the upper RPM regions either. for a heavy B body, and my preference for being stealthy, this is the cam I'd use, especially if you plan on keeping highway friendly (2.76-2.94) gearing.
comp 268H 268/268 adv, 218/218 .050, .454/.454" lift with 1.5's, .484/.484" lift with 1.6's, 110 LSA, 48 degrees overlap. would probably fall somewhere between the summit cam and the XE256 in idle quality and performance.
for reference, I have a stock long block 360, some home bowl ported 360 heads, headers, eddie air gap, 600 eddie carb, and a comp XE262 in my 3900lb 5th ave. I used the head gaskets out of the standard felpro gasket kit (.054" compressed), my calculated compression based on my pistons depth-in-hole is about 7.8:1. my car idles with about 13" vaccuum in gear at 750 RPM (17" in park at about 900 RPM) so it has a very slight lope. my 3900 lb 5th ave, with an A500 tranny, 3.55's and 27" tires moves very good, and can keep up with a LX 300C hemi from a roll, so I'm guessing it's a low 14 second car, maybe nipping high 13's. the XE262 has too much lift on the exhaust lobe for your springs, but the 268H should perform nearly identical (if not better) with the mag 1.6 rockers as an XE262 with the LA 1.5's
