68 Barracuda. How Big Can I Go? Rim and Tire?

I had 295 50's on my 69 Formula S in the Avatar but I had to use spacers and long studs to accomplish that. Also put Hemi springs on it so it sat really nice. Trying to use all stock stuff will be a different animal. This 68 I have is very original and I want to go back to the stock setup quickly at some point so I don't want to do a bunch of mods. to get the look I'm after today.