I put some Roush side splitters on my car and it stopped a lot of the rock kick ups. I also did the rear splitters and really like the look of it because it ties the black from the the black on the back.
As for tires I just went and bought Michelin Pilot A/S 3's for mine. They are one speed rating down from stock. They have a better ride work better in wet weather and cold weather. I do not race mine so the speed rating was not a factor to me. I wanted a streetable car in cold to hot weather. Just got done running 1500 miles from OH to MO and back and I am glad I went this way.
1968 Coupe <53000 miles on her 289 came off the line Jan 21st 1968. I bought it in 1983
2013 Shelby GT500 Born 12/06/2012 number 439 of 530 in DIB and 1 of 9 with Red Stripes over the top and on the seats