What back spacing on wide rear rims....

[bigcowl-imp]

Just picked up a 64 chevy short fleetside and it came with the fat wheel tubs and i checked and i have 16 inches of tire clearance......I`m thinking a 15x12 rim with 7 or 8 inch back spacing maybe ????

The rim thats on there now is a 15x8 or 8 1/2 wide.....with a 5 inch back spacing..and i have 6 inches of clearance on the inside and about 1 1/2 clearance on the outside......sectional width on the tire is 10 inches...

So watcha think and thank you for any help...