Well, between not having any time and not wanting to spend any more money, we've just kept driving it. We've put about 1200 miles on the engine to date. Right after the last post, I decided to go ahead and try some Restore - $8.40, vs. $100 for gaskets & bolts to swap the heads. I've also been running a 6x dose of AMSOIL gasoline additive.
Amazingly, it does seem to be getting better. It still is a little rough at idle, but it is a lot smoother than it was before - I hope the cat hasn't been wiped out with the misfiring. Power is now as good as or slightly better than the LN3 was, although the '91 LE still is peppier. It'* hardly used any of oil since I added the Restore, having used about a fourth of a quart in those first 500 miles.
I don't know which is helping, just running it, having the synthetic oil in it, the Restore, the gas additive, or a combination of them. We may never know. I should have repeated the compression test before putting in the Restore, but again, no time. I hope to repeat it some day soon.
I've been thinking the engine had been sitting outside after being removed from the car with the MAF and exhaust manifolds open, three cylinders had a valve open, so those cylinders/valves corroded. Running is cleaning it up. Of course, I could be all wet.
Bottom line: If your LN3 is getting tired, and you find a good L27, this project has shown it will work with your LN3 induction.