Biggest wheel on an 8 3/4 early A?

I've got the same rear end setup with leaf springs on my '68 Dart and I don't think I'd be able to fit anything larger than a 9" wheel under my stock wheel wells. Granted, I'll be running an 18" diameter wheels so I'll be getting much less tire flex than you will with a 15" wheel. I'll be running 255/40/18's on all 4's.