Rear Tire Rub

[bulldog19]

I have a 68 Camaro not mini-tubbed. Wheels and tires were purchased from a supporting vendor here. On the back I have Rushforth Superspokes 18 x 9 w/275/40's and the fender lip is rubbing the outer edge of the tire. I have ground the edge of the fender lip to try and gain some room but still rubbing. I'm cautious of any further use of the grinder for fear of going through the weld between the outer and inner fender. What are my options here?
Rear suspension is Hotchkis TVSS.
Do i need to just go to a narrower tire? I hate to cause the stance is spot on with the 275 in the back.
Would a stiffer shock/spring help?
Can the rear be raised 1/4-1/2" easily?
I don't think i need much judging by the marks on the tire from where the fender lip has hit.
Thanks for any insight and suggestions.