70 RR 15" rally wheels..... which is correct? One set from Summit... one from Mega parts... or does it matter...??? Different size....

The one on the right is the correct 'style' for rally and road wheels, and come in different lengths. However, the new "bulge: style on the left give significantly more contact area for wheel retention, especially with older wheels which sometimes have oval'd or misshapen holes due to years of slamming the lug nuts on by overzealous impact operators. I literally just replaced the OE nuts on my 71 Cuda (with 15 X 7 rally wheels) with the ones on the left. Won't pass a muster for concours judging, but they look darn close to original, and the fresh shiny chrome gives a nice overall appearance IMO.

Thanks! Just checking since they were different... not a concurs guy anyway.... lol

back in the day, it was common to replace the original nuts, chrome or plain with ford nuts because they were 13/16 instead of 3/4 to fix ovaled out holes.
this was ONLY possible on 71ish up, with ALL right hand threads.