If you're going with a newer V6 Vortec, you will have to make a few changes, for one, there will be no exhaust gas passage in the intake manifold to heat the choke spring. So if you have a 4bbl Quadrajet and want to keep it, you might re-search how to convert this to an electric choke (I've seen stuff on this out there) or use a Holley 4160 in its place (there is a specially calibrated Holley 4160 for the V6 OMCs and Volvos that originally used this carb when OMC stopped using the Q-Jet back in '90 or so). The other is the electric fuel pump. No provision for a manual pump on the newer Vortec block. The only other thing is the shift linkage bracket that bolts to the last 2 intake manfold bolts, on the starboard side. Due to the fact that the angle of the intake bolts on the non Vortec were at an angle, and the Vortec bolts go straight down, this bracket may have to be bent slightly to make the shift linkage fit.
With respect to the exhaust, yes you can no longer get the OE one piece manifolds, and it is not hard to convert them to the newer center riser style used by both OMC and Volvo. The only piece that is pricey is the 90* adaptor elbow that adapts the 4" riser hose to the 3.5" OMC/Volvo style Y pipe. This part is available from Volvo (pricey, about $200 each) but you can get a cheaper version from GLM. I used Volvo because in salt water I won't use cheap exhaust parts. The rest of the system you can use Barr Marine aftermarket OMC/Volvo 2 piece center riser exhaust parts. I did this when I did my top end overhaul on my '88 4.3.
While you can find places selling the GLM 2 piece conversion for the one piece system, the quality of their machining has been below par in the past. It may have improved but I did not want to take a chance so I went the more expensive route, made in USA Barr exhaust and Volvo OE 90* exhaust pipe adapters. I also used use the Volvo exhaust hose. Now when it's due for the next replacement in 5 years all I need is the Barr manifolds & risers.
BTW, used 3 sets of batwings over 15 years of moored in salt water boating and they never leaked. Had a bad overheat back in '13, still did not crack or leak.
And while the OMC Cobra may be considered 'obsolete' I prefer it to the Alpha, because the transom mount assembly is not prone to the leaky steering arm issues, or the worn hinge pin issues that happen on Mercs, the bellows is easier to replace, and the impeller is MUCH easier to replace. Once you learn how to set up the shift linkage, it is not the mystery some make it to be. I taught myself to do this in a few hrs using the special tools (still available) that are out there. As long as I can get parts and I have 2 mechanics here who will work on Cobras, I'm keeping it. Have had very little trouble with it over the years, in a tough environment for sterndrives (moored in salt water use).
