They're about $60 by themselves if I remember correctly (the Sy pumps) but you'd probably want to replace your in tank harness too, and replace the piece of rubber hose and need a new tank seal, etc. so by the time you're done you're talking about minimal savings.
http://www.racetronix.com/product/RX..._ L98_Pump_Kit
This is the racetronix kit which is a significant upgrade in the harness as well, I built something like they did using an old relay socket and a fuel pump relay from a JY harness. The Buick guys call this "hot wiring" the pump. The big deal is that the main run of wire is #10 to the alternator terminal, this can be worth significant capability in the system because the voltage doesn't drop off at load. The old fuel pump wires are used to turn on/off the relay which in turn turns on/off the pump. I believe they also run a heavier ground as well, but don't me to that.
The difference between a 307 and 340 is largely how much boost you can run, because you have base FP+boost level, the 307 bypasses at ~60 PSI the 340 doesn't. That means assuming a 43 PSI base ful pressure you could run ~17 PSI boost. The 307s are good for about 550-600hp generally, so unless you're running a super racey setup it should be a good pump.
http://www.fullthrottlespeed.com/cus...kc~834GMHP.htm
This is $99 with the install kit, I'd call up and ask but it should fit your application as well. You can't go wrong with Mike, he's a good guy. For the extra $$ I'd just get the Walbro btw.
