Custom Harwood Install

I am recycling some antique fir hardwood flooring. I will convert the original 3 1/2" tongue and groove 3/4" thick planks into 2 3/4" T&G, 1/2" thick planks. That's the only way I can salvage the original stock.
Two questions:
a) Is there a good alternative to the tonge and groove configuration for hardwood flooring? (like concealed fastener system and square edged stock.)
b) I'll need to plane down the thickness of the boards. Can I runt the batch at the maximum possible thickness or do I need to aim at some industry standard, like 1/2" or 5/8" in order to use a nailer like porta-nailer, or the like?
Thanks for your comments!

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