[jarretts70]

I agree with i82much.....take a breather, Walk away....come back in a couple days (or weeks) with a clear head. Then start with the basics - drain the oil & look for metal. Buy/borrow/steal a scope you can stick in a spark plug hole to look for debris or other carnage. (they are cheap on amazon if you don't have one). Crawl under it to make sure it's actually in neutral - there is always a chance there is a issue with a new clutch / pilot bushing / throwout bearing causing the trans to hang in gear.

I has similar feelings as you a couple years ago - freshly rebuilt 428 in my Trans Am began to run like crap, smoke, misfire.....I assumed the worst & was getting ready to pull the motor when a member here suggested 2 things: 1 walk away for a could days. 2. Check the valvetrain. Sure enough, a rocker had backed off...tightened it up & everything was just fine. You might not get that lucky, but there's a chance it's not as bad as you fear.

[STEELCITYFIREBIRD]

S

All or some plugs have gap closed?

Correlate to one side of manifold?

Mechanical contact obvious?

I would pull the valve covers look for anything obvious.
Remove all rockers and look for anything obvious.....valve/s open or hyper extended spring,