RE: McCoy diesels
Dan Vincent here.
The McCoy tank screws were a bit wider than the Wasp, Atwood and Spitfire tanks but the OK Cub .049X and Holland Hornet were a bit wider. I don't know off hand if they will fit into the backplate hole of the McCoy or not.
I do know a McCoy Baby-Mac .049 tank will fit but the Baby-Macs are pretty scarce.