Now I need the ongoing guidance about intake and carb. I have read that there is no GM 4bbl vortec intake, only aftermarket intakes that have iffy reviews. That is unfortunate, because I have 2 quadrajets...
not true. GM offered many 4-barrel cast iron intakes for the vortec head. just not on any vehicle. only thru the performance parts division which is where the marine people picked them up. however plenty of dual alloy marine intakes out ther. by dual alloy, there is bronze in the water passages, and aluminum for the majority of it. this was first developed by Buddy Barr for PCM back in the 80's, then adopted by Volvo, Ilmore, etc.
instead of cast iron, I would get a dual alloy marine intake. its about 35# lighter than the cast iron intakes and most perform better. I picked up mine new on ebay a while back for about $300
if you want cast iron, Michigan Motorz keeps them in stock, as well some of the dealers that do a lot of GM performance parts. too bad Sallee Chevrolet wasnt still around, you could get a complete package deal on heads and intake for cheap. Plenty of ebay vendors have them as well most of the new cast iron intakes for vortec heads and a 4-barrel are about $330-350. aluminum is less, dual alloy castings more on ebay. however this is something that I would have no problem going used.
if you switch to fresh water cooling now, you could simply go with an Edelbrock RPM air-gap intake which will help the SBC in the low to mid-range. it would also keep your motor around for a long time, as you wont have to worry about cracking the block or running in salt water.
My main goal is reliability and efficiency.
if you are looking for efficiency in a boat, get a sailboat. your boat will burn 0.4 # of fuel per hp per hour. since you have a 26' boat, you will be commanding a lot of power to move it along.
you can get more power from the SBC with a cam change. the truck motor will be a roller motor. a XM264HR or XM270HR cam and 1.52:1 roller tip rockers would wake the motor up. no need to spend money on full roller rockers, the $60 for roller tip is what I would recommend
however you mentioned you are having your heads machined. get an estimate prior to having work done. new fully assembled heads are $500 a pair, yes that is $250 each for vortec heads. also, ask about converting the pressed-in rocker studs to screw-in as well as having the heads machined for higher lift cam. this will be required if you change cams. that service alone should be about $100 (50 for cutting the spring seats, $50 for converting to thread-in rocker studs)
