I found this about springs...

http://www.alexsparts.com/valve-spri...rf-hyd-roller/

Those were the springs I used.

As far as looking for heads, find a dirt track guy that has blown up or replaced a 602 crate motor. you can get the heads and intake all in one shot, and those would be vortec heads.

Done this about 3 yrs ago. Ditch the gm heads and find a used set of dart iron eagles or sportsman 2 heads. U will be better in the long run. I used flat top pistons dart 200cc heads same 262h cam u are talking about with a dual plane high rise intake with a 750 holley. I picked up 6 mph with the rebuild and upgrades. I used a set of 1.6 rockers I had. 10.2 compression. Ran real good but as always it was replaced with a 396 small block in favor of more speed! !
In my opinion vortex heads are not much count. They need lots of work to make what I would call good power. Give me a set of old double humps over vortec any day!!!!

Vortec's are better than the double humps. Sorry.

They have a raised intake runner and very modern combustion chamber.

Off the Vortec's for a second....

I picked up just about 15 mph with reusing the stock million hr 1991 5.7/260hp short block. Pan never came off.
Decent heads - Bodix IK180's. They are nothing real special compared to AFR's. Vortec's in this application wouldn't be down more than 5-10hp.
Can run 87 octane.

So............

Double humps were great heads....In the 1960's.

You can see evidence in the timing. Vortec's only need 32 degrees, that is indicative of a faster, more complete combustion event.

The successful small bloc recipe used for seemingly forever is:
stock decent condition 5.7 260hp short block
Vortec heads (not ported, no bowl work. Yes on spring upgrades)
RPM intake or Air Gap
600-750 Holley
Comp 218/224 112LSA Marine HR (some have used GM Hot cam 218/228 112LSA)
GLM exh maniolds with 8-10" SS inner tube extensions (some have done this to stock exh manifolds)

Boom. Done. Even non performance hulled 20ft boats have picked up 10mph. Performace hulls 12+mph

You'll find a lot of small block builds and real world results here:
http://www.speedwake.com/forums/showthread.php?t=27967

Well my boat is a 20ft Cobia bowrider. I was planning on a RPM style intake, but I don't want to re-make the engine cover I just finished. I'm close now with the flame arrester, but I could come up with something.

Yeah take a walk threw your local dirt track pits and look for vortecs. Only place u will find them are in the crate class. They are junk. SB u are a bmfer. 15 mph with crummy brodix in heads wow. There just as sucky as vortecs. U are my hero. Think u can help me hit 200 mph in my 85 chevy dually with a 305 on 87?

Yeah if u wanted to put it in a dump truck! Let's see 10 hp equals about 1 mph. So 10 mph more would be about 100hp! Your flipping dreamin. I have been there don't that with vortecs. With that baby cam no way u can make 360 or so hp. Not going to happen!!