Every spring before the season, I remove and pressure test my headers (all 6 of them) for leaks and every year, I wrestle with getting the two inboard headers on the two rear engines back on. Getting those header bolts started and ensuring they don't cross thread while trying to maneuver the socket wrench and not drop the bolts into the bilge is always a challenge and due to the angle of the inboard port engine header, there are two bolts that take forever to get started and I usually end up with bloody knuckles. I use two headless bolts on the end holes to hold the header while I get one or two bolts in and that gave me the following idea.

I was thinking of screwing 3/8" stainless steel fully-threaded studs into the head, dropping the header in, and then securing with serrated flange nuts torqued to the same value as the header bolts normally are (ie: 35 ft/lbs).

Is there a reason(s) that this wouldn't work or is a bad idea?

Yep, Id do it on all three engines, that's why the header gasket is notched, slide the header on start the outside nuts and drop in the gasket from the top and it rest's on the studs

F2- Speedy is all over the answer. Also switch out the bolts to STAGE 8 LOCKING BOLTS. Then they won't loosen up throughout the season. They stay tight. Just my 2 cents

Just to be clear, are you saying that you agree that I can do what I'm proposing?

Great suggestion, although loosening bolts has never been a problem for me. I'm also trying to get away from using bolts; that's the whole point of using studs and nuts.

yes, install the studs in the outer two holes in the heads

OK, I should have been clearer in my initial post. What I'm proposing is using studs in ALL 8 (per side) of the holes in the head, not just the outer two.

The complications I can think of are whether there is enough clearance between the bolt holes on the header flange to accommodate the increased width of the flange nuts and is their enough room to get a 9/16" socket in there versus a 3/8" socket.

I see, if you have the clearance on the tubes, those CMI sweeper headers tube angle get tight on the left bank

Wouldn't it be easier to just leave them on and pressure test with air?

I see no problem with the idea. But clearance for the nut (and a wrench/socket) will generally be the problem with this idea. You may look at ARP for a solution. I think some tubes will be ok, but others are going to require a bolt with small head.