You're not really going to see performance gains with air filters on a TR3 like you would altering a stock airbox configuration on a newer vehicle designed to be quiet and restrict flow for longevity.
Also, I wouldn't really be too worried about longevity on a TR3. The engines can last 100K+ miles with the stock air filters, and let's face it -- most owners won't put one-fifth those miles in the time they own a TR3 these days. Heck, I think I have only 500 or 600 miles on mine in two years.