at this point almost all spur gears are universal for touring cars and can be interchanged. kimbrough, xenon, prs, rp racing are some common brands.
you dont have to switch from 48P to 64P, this has nothing to do with what gear ratios you can run or cant run, its a preference to the type of gear mesh you will have. 64P requires a good understanding of gear mesh so that you dont strip the gears, although they are easier to strip anyway because they have less teeth engagement. 48P works fine and will just be louder.
the stock 72 will fit up to a 36 tooth 48P pinion. to get a 38 tooth in there you will need to run a smaller 69 tooth spur for 48P.
hope this helps.
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