What size tire for 3/4 dropped C20?

[earl84]

Making slow progress. Today is the purchase of a new Edelbrock 1406 carb and assorted goodies.
When I bought the '66 C20 it had 8.75 X 16.5 dry tires on it. These are hard to find and usually expensive and I want to be able to get a replacement easily should I ever have a blowout on the road. Going to keep it 8 lug 3/4 ton and eventually do a static drop of 3" in front and 4" in back and replacing the front crossmember with a 73-87 3/4 ton crossmember and eventually the rear axle with probably a 14 bolt rearend. Yesterday I bought some 8 lug 16 X 7 inch rims, which are getting sandblasted today.
Anyway, the real question is what size tire will work on this drop without clearance issues?
I stopped at a tire store yesterday and a 255/70/16 is close to the original height, but wider. It looked killer, but again, I don't want to have clearance issues later and only want to buy tires once.
Thanks in advance for any help. I need to start taking a few photos. Lots of little things have been done already, dying to get it on the road.