If I was to run 6's on rear and wanted to try 7's. What difference in spocket teeth would I need to run (2)

i would try 2 teeth smaller(less) as your diameter will be smaller,provided u use the 210mm(8" wheel.

After mounting tires, set to desired inflation. Measure both tire/wheel combination's circumference. Now take the present number of teeth on your rear sprocket and divide it by the number of teeth on your clutch. Multiply that by the circumference of the 7" tire. Take this number and divide it by the circumference of the 6" tire. Take this number and multiply it by the number of teeth on your clutch to get the number of teeth on your rear sprocket for the 7" tire.

thanks