Still haven't figured out the idle issue...

^^I understand. But what timing were you running?

I assumed the 850 was a requirement to satisfy a big cam.
And to have a big cam, 5* idle timing, and still pull 20inches;Hmmmmmmmmmmmm
That's a pretty good ring-seal

I've had a few stone stock slantys that wouldn't pull that off. Not oil burners either.
My last slanty does tho. But it's not stock.
And no, I'm not arguing; I just can't see it, based on my very limited experience.

FWIW;stock slantys can idle real good at 450 to 500 in gear. I love it when you can count the shots, ,and those shots start to shake the car,and the sound in the pipes go "thoop,thoop,thoop."
Oh and I've had better results at 13/23 lash;splitting hairs I know.