They are available in a 295/50-15s but they HAVE to have 10 inch minimum rims.
To get the tires to run flat to the road, mine are down at 24 psi on those 10" rims. I can feel that on the turns as the tires roll onto the sidewalls. They really need 12s,but I'm used to it, and the sidewalls don't actually touch the road. But it sure feels funny.
Mine is a 68 Barracuda with factory tubs, offset springs and a narrowed rearend.
BTW
295s on 10s will be about 13" cross-section, or a bit more,and you will need a bit of extra room for the tire/spring roll-over.
It will take custom offset rims to fit those into your tubs. I narrowed my rear to the max to be able to fit 4.5bs rims
If you run them on 8s, you will likely have to run down at 20 psi, to get the treads nearly flat to the road, and the centers will not wear at the same rate as the edges. They will be wearing all wonky on you.And zipping around corners at 20 psi, is scary to say the least. I highly recommend that you rethink that idea.
275/60-15s can be installed on 8.5s and run at 28psi. That corners a whole bunch better. And 275s do a pretty good job in straightline work. And you are not limited to BFGs, which only have traction for the first hour,lol.
275/50-15s want a 10" rim too, but I have run them on 8.5s with reduced tread life.
The only reason I am running 295s is for the cool-factor. Well, that and finally the back stays in the back when I powerslide around the turns; I love doing that.