Update...
I just finished the HEI conversion this afternoon (hey, gimme a break... wife's been in the hospital). The result? No love at all.
Oh, and that noise? It's back. Well, then it goes away again. Then it's back. Now that I've heard it come and go all while the engine's running, I'm thinking I've got a lifter acting up on me. Grrr...
To make matters worse (or better depending on how you view it), I noticed some fuel (not much, but enough to get my attention) down by the driver's side front near the idle screw after kicking the engine up to about 2500 rpm for a minute. I'll be giving my carb rebuild guy a call in the morning about that one.
Somebody want to sacrifice a <bleep> chicken for me? Geez... my freakin' inspection sticker's gonna run out before I get this thing fixed at the rate I'm making progress!