I run the 275/60-15's on my '68 Barracuda convertible with V-rated(149mph) General's 215/60-15's on the front. These are still available. This car currently has a bit of predictable over-steer that I'm comfortable with.
The '70 'Cuda has the 325/50-15's out back with V-rated225/60-15's that are no longer sold by BF Goodrich. There are several other V-rated tires in that size range available including the very expensive Pirelli tires that are direct replacements for some of the older Porsches.