The aftermarket support for the 4.3 is not good. There are cams, intake and some exhaust. No heads unless you count 18 degree from gmpp or other high dollar heads if their still available (3800 rpm and up power band), no cranks. This has all been hashed over previously- do a search. DV has as much experience w/the 4.3 as anyone on this board. Ask him what he would use to go fast on a budget, naturally aspirated. If he says a 4.3L V6, then there you go.
If all the OP wants to do is run a number, in this case 128 mph- he might be able to do it w/production Vortec heads and some porting along w/a cam. But if he wants to get a better return on his money, bite the bullet and do the V8 swap.
You make it sound like $1500 for a swap puts the idea totally out of reach. It's MY opinion that it's the best $1500 he could ever spend if he's really serious about going fast. If all he's trying to do is get some kind of bragging rights that he can go 120-plus then, again, so be it. But doing a swap opens up an almost unlimited amount of cheaper hp than you will ever get from a 4.3. EVER.
I don't know how or who builds your SBC 350s that they make only 180 hp, but stick around and listen- you will surely learn how to make a hp/ci on nearly the same money it takes for a stock rebuild.
I currently own two 4.3s, so it's not like I haven't looked into them.
Last edited by cobalt327; 12-08-2012 at 04:48 PM.