what size notch

i just picked up a 85 720 and im gonna do it old school so no bigs wheels so what im trying to find out is what is the smallest notch i can get away with to lay frame with either a 14 or 15" wheel with white walls

Get a tape measure out and measure it up. How far is the frame from the ground? Now measure from the axle to where the frame is now above it. The difference is how much it needs to be notched. You might have to work with this a little depending on the size wheel/ tire you go with. I usually ad an inch for safety, if the front is up, back down it might hit. Best bet would be to notch it for 17's with a lo pro and then you can always change the wheels when you get tired of the old school look.