365 Mag engines have 224° single pattern FT cams with 0.510" lift. 115.5° LSA. Not a bad Supercharger cam.

They were 390hp at 5200 rpm at the crank.

The 088 Rec Port heads are less than stellar. Quite honetly you would be better off with wrmed over Peanut Port heads. 70s/80s PP heads vs the 90s Gen V style.

You have 0.095" domed piston. The piston quench decks are poorly cast and can vary in their 'flat' surface. Generally in the 13cc dome volume.

8.6 CR

They also used a firm mounted rocker stud system, where the lash adjustment would be in the pushrod sizing. Aftermarket rocker studs are available...but had 3/8" studs into the head...and 7/16" on the rocker threads.

The stock cast iron exhaust manifolds can flow a reasonable amount of air. At 2.2cfm per hp unrestricted, they allow for about 415hp. Anything more than that they'll be a progressive restriction the more you ask from them.

Small SCs will heat up your air more at higher airflow. You can get diminishing returns very quickly.

If you SC....a quick bore hone (0.001" more) and re-ring would open up the piston to bore a bit for the extra heat expansion.

Valve health is another story. Re-building the rec port heads won't be cheap. Going to an aftermarket 290cc alum head ($1500 ish bare+ good parts) would go a long way to solving your problems. SCs + setup are not cheap, and you'll use more fuel per hp than NA.

wouldnt 1988 mk 4 454s have normal rocker studs, not "firm" non adjustable 3/8 thread ones ones as you mention?

Yes sir.

Smitty, that's right. For some reason I ended up thinking it was a '92.

If you are not going to upgrade your exhaust, you are wasting your time. You can't do any decent cam upgrade without upgrading the exhaust. Exhaust is building block #1.

Yes but exhaust is expensive and almost as much as a used set of 174 superchargers, but yes I get it.

You can push extra ait into the cylinders while compressed, but that extra volume needs to be evacuated through the exhaust. The restrictive pumping losses add up very quickly....to the point the SC may not add any power at all.

You didn't mention a HP goal. Very difficult to have success without specifying the goal and mission.

500hp, you're going to need some exhaust. The twins makes that reality a lot tougher for sure. Harder to find double used parts etc.

If your exh manifolds are any good at all...they'll have some value to re-sell...otherwise you need new ones anyway.