That is the same intake that was on my 1993 454mag with a weber carb and no adapter was used. I also looked it up on mercruiserparts.com and the 7.4 used the same intake for several years in the early and mid 90's with no adapter as well.

Great info. Thanks.

Busy start to my week. Thanks for th info about th carb adapter and the subsequent verification of it not being needed. Short answer, no, I don't know what was on this motor originally.
I was too busy to stop by or call mechanic today but he did do compression test as I asked and he texted me that all holes were at 180 psi.
We are still chasing down a leak in the transom, we think it was the trim Manifold gasket at the bottom. Had a ***** of a time getting it out and of course the new one showed up with a chunk taken out in one of the 4 holes that definitely wouldn't have sealed properly and leaked so we sent it back and hopefully the new one showed up today. So next thing he wants to do is more carb troubleshooting on the water. I'm really feeling like some random carb problem is the culprit and really just want to buy a new one and stick it on but again new ones can't be had right now. Trying to source a known decent working one to test.

Those are sold already

took the carb back to the rebuilders under warranty. They took it apart and send there was some funky gelling in there and cleaned it back up. Bringing it back to mechanic tomorrow and hopefully we can get her out again and see whats what. Will probably top her off with fuel again to get the octane up and make sure it's all fresh fuel

Probably the Ethanol goo (it also crystalizes) from sitting. How long did it sit again ? Aluminum or plastic tank ?

Tank was filled in January 2021 and a gallon of seafoam was added at the same time. Got little use beyond seatrisls and occasional running every couple of weeks while I worked on other cosmetics with the boat. Then boat blew up in September. Carb only had 5hrs of use after carb rebuild before motor blew up. Carb sat on shelf from September until January. Fuel has come up out of tank looking good everytime, no water that we have seen. It's a plastic tank.

After watching the video I gotta say I'm impressed with the power potential with the head/intake port mismatch. Just bumping up the cam made a nice increase. For me, I'd have to go to a forged crank and bigger rods of the Magnums if I added more cam, RPM, and HP. The dyno numbers are great but I like reliability. A boat runs at constant high rpm for a long time while a car rarely does. But I'm surprised that the potential is at least there.

SB is on point. I’ve seen carbs get the jelly goo looking junk and crystallized stuff in just one season. Hope that’s all of your problem.