If you putting those on the 8" wide Welds, it'll be just fine. A little bulge. Nothing to worry about. I just wouldn't put them on 7s.
So many times I have seen 26x10.5x15 or 28x10.5x15 on 15x8" (that's what most people use--from what I've seen--if they buy Welds) Welds and no real problems. I've even seen those 275/50/15s on 15x7" rims on a GN. Now that was too bulgy for me, but on 15x8 (they are "offically" rated for at least 8.5" wide rims, though) it'll be okay.
-----------------------------------------
'79 Mustang Coup w/ 4" Cowl
Stock 5.8L, C4 w/ shift kit
Holley 750 cfm, Edelbrock Performer RPM intake
1 5/8" MAC shorty headers, Al driveshaft
2.5" Off road H-pipe, 2-chamber Flowmasters
Front: 225/60/15, Rear: 255/60/15 Eagle GT II
Weld wheels (15x6;15x8), 8.8" Rear w/ 3.55s
14 x 4” K&N air filter (getting the Xtreme setup someday)
"Red, thou art my companion. Hasten now your quickened metamorphosis to
Green that I may conquer all who dare abide there beside me. May they be left
thither behind burnt black." ---Fox Body