440 spark plugs

[jlcoffell]

Anybody out there know how I can find the right spark plugs for my engine ?
First off it was originally in a 1969 GTX. The date stamped on the block is 66 and has C440 stamped on the front right pad.
The engine has been rebuilt and modified and now supports the following:
11.1 to 1 forged dome pistons, cromoly (? not sure spelling) rings
crane fireball cam at 4 degree's adv., edelbrock performer intake, carter 625 afb (note: problem was still there when I was using a edelbrock torker with a holley 780.
My problem is that I am so far off on the heat range that the plugs are almost unreadable when I pull them out.
I will install Autolite 85's which is what the book calls for for both the standard and high performance engines for that year.
It will run decent for about a week then start missing at low revs.
I can't remember all the different plugs I have tried but the best so far have been NGK small engine plugs (don't recall the number).
The Autolite 85's come out looking almost silverish with what looks like small particles attached to them. All 8 look almost
identical.
Not engine problems as engine was built and first fired up 1982
still runs good as long as plugs are changed weekly.
The small engine plugs come out with the ceramic cone being
a cross between white and light tan. Close but still a little to hot
and the small engine plugs are so short I have a hard time keeping the spark from jumping to the headers.
Any ideas????
Thanks in advance