The speed rating has nothing to do with traction. The speed rating is a function of how much heat they can dissipate which allows them to run at higher sustained speeds without failure. Typically for the same size tire the higher speed rating will have a thinner side wall and will need to be run at a higher pressure. Also, the tires with higher speed ratings typically will have a more agressive tread patten which will make them noisier too.
Probably the single most popular tire for old muscle cars is the B.F.Goodrich Radial T/A. This is a good all around street tire; smooth running, quiet not great for straight traction but OK and is about the only tire that is still available in all the 14" & 15" sizes. Unless you have done a lot of suspension upgrades these tires are better than the suspension of your car.
I currently have Radial T/As in 225/60-15's for the front and 255/60-15's for the back on my 68 Barracuda. Prior to that I had 235/60-14 Goodyear Wingfoot HPs. Goodyear, Dunlap, Firestone, Cooper still all sell and equivalent tire to the Radial T/A but don't have as many size choices.
If you are really in need of an H speed rating or higher then you will have to start looking at 16" or larger rims.