Engine Run-on help. (dieseling) I promised I searched first.

[jorgensensc]

I promise I searched first, and read a bunch of responses, but they don't quite fix the problem for me.
Background: I just installed an engine for a friend. I didn't build the engine, just installed it. It is a fresh rebuilt 350 .60 over, with fresh rebuilt 305 heads (I didn't build it), and an RV cam. Cast iron intake, fresh rebuilt (by me 2 days ago) Edelbrock 600 electric choke carb, Skip White HEI (pulled off the former 350). 4 speed manual (granny low).

The old engine burned alot of oil, but ran okay when I pulled it. It did not run-on at all. Drove it around quite a bit, and never had an issue. It sat for about 2 weeks while engine was being pulled and new one was put in.
Engine runs fine, doesn't overheat, no misfires, nice and smooth with no stumbling.
However, when ignition turned off it continues to run-on.
I have adjusted the air/fuel mixture to where it is good (3 turns out both sides)
I have adjusted the timing, from when it won't start (retarded) all the way to past hard start (advanced) in 2 degree increments all day. (Vacuum advance plugged)
The idle screw is turned all the way out to where it doesn't have any affect on idle.
Even with the timing almost fully retarded (lowest idle possible) it diesels. as I advance the timing to where I think it should be (between 8-14), it idles way to high. I cannot adjust the idle screw anymore and hav it have any affect on the idle speed.

Do y'all have any suggestions? Would the engine specs have anything to do with it. Is it possible that the low grade (87 octane) that is in the tank won't work on this engine and she will have to go to the good 93 octane stuff? Is the compression really that high?
Any help would be appreciated. I'm ready to get this thing out of hear so I can work on the Burb again!
Thanks!
Shawn