72-spoke wheels are MUCH stronger than 48-spoke. I don't know why they even used 48-spoke wheels on the 6-cyl cars (cost, I suspect). The later cars came with 60-spoke wheels. My BJ8 had the original 60-spoke wheels and 185/70X15 tires when I bought it. I put new tires on, same size, and started breaking spokes, so I got 6-inch, 72-spoke chrome Daytons--no problem with broken spokes. I now think 6-inch rims are a bit too wide, just because they stick out of the wheel well too much. 5.5" or 5" rims with 175 tires would be about right for appearance, but as noted 175-width tires are essentially unavailable. The 185s are getting hard to find, too; the best option being Vredestein. One Healey owner has 185 (not 70-series) on, I believe, 5" rims and is very happy with them. They are taller and 'narrower' than the lower-profile 70-series and closer to original tires (although the 185/70 Vreds are close to original diameter). I will seriously consider that option when I'm due for new wheels and tires. 5.5" is available, too, but only from Dunlop which had a bad reputation but I hear they've gotten better. There are some differences in the hub between Dayton and Dunlop (I think the Dunlop is closer to original).
If you like to corner reasonably hard, you'll want/need 72-spoke wheels.