I got all new stainless header bolts @ https://www.boltdepot.com/
Great prices, fast shipping.

I always like to let them go thru a heat cycle and while they are still warm give the bolts an extra quarter turn.

You could use blue Locktite or a non-metallic anti-sieze.

Ayuh,..... I was always an Anti-seize kinda guy, 'n have used mostly the nickle based anti-seize on 'bout anything, 'n everything, bein' a heavy equipment/ heavy truck Mechanic by day,...
Of course, as I transitioned into Boats over the years, I also carried with me my Anti-seize habits,...

'n bein' a freshwater boater up here in the sweetwater seas, I never had much of a problem with corrosion anyways,....

Over the years I've been postin' at iboats forums, I became very good friends with Don Sindledecker, the rather famous Don S, who unfortunately, pasted away 2 years ago this July,......
Don spent most of his career in Ketchican Alaska, movin' down to seaside Washington state for his last few years,....
Anyways, Don S was a Loonnngggg time Saltwater boater/ Mechanic,....
Don S always called Never-seize, Ever-Seize,....
After much discussion on the matter, I tried Don S' routine, which is to coat bolt threads with,... Quicksilver Perfect Seal,... aka: Form-a-gasket, #3,.....
Now that several years has past, 'n I'm removin' bolts I bathed in Perfect Seal, insteada Never-seize, I can tell ya,.....
Perfect Seal, seals the threads, 'n pretty much Stops corrosion,...
Much, Much Better than Never-seize,....

While I still use Never-seize on occasion, Perfect Seal, aka: Form-a-gasket #3 is my "Go To", rather than Never-seize,....

I have been using grade 8s on my gils for 6 years in fresh water with no issues at all

The stock bolts that came from Merc with Gil exhaust were SS Allen head socket caps.

And stainless and lowes grade steel bolts are just as dissimilar to aluminum anyway.

Most of the hardware stainless bolts around here are as soft as chapstick. Buyer beware.