tire options left in 14 inch ?

Well if you lived next door I would roll 'em over.

I think the WheelVintiques 15 x 8s,sbp, I ordered were about a $100 to $125 Usd each, in primer, with the custom spider install, in year 2004ish.

While the 275s will fit on a spec rim of 7.6 inches, I find they wear very nicely on 8.5s, and can run pressure of 24 to 32 no problem. I used to run them all weeh(DD) at 29, and then air 'em down for the weekend.
At 29Plus they corner pretty good. At 24 they stick better on the straights. At 32 they might save a bit of fuel on long trips.

If you install them on 8s, Ima guessing, it would be a bit of a compromise.Keep in mind also that a 275 is only a 275 when mounted on a rim of 70% of 275, which is the checking rim of 7.6 inches. On an 8 inch they will be a tad wider. Ima guessing 282, which is a section width of 11.1 inches. On an 8.5 they might be 11.4inches.
The limit in your wheelwell is not rim size. It is section width to springs, and section width to lips, and tread to front outer corner, and tread to the odd shaped curvature in the tops and fronts of the inner liners.
If I had a 408, I would be trying to fit 295s in there(they fit in my 68S).
But if I was not able to fit those, I would absolutely for sure be moving the springs over with the 3/4' offset hanger kits.This is cheap and easy and is good for 19 more millimeters, and it's all to the inboard side. Since other guys here IIRC, have successfully run 275s on Dusters, I imagine you can too.
The 70% checking rim for a 275(10.8section) is 7.6. The 60 series like an 8.5 rim, but I suppose an 8 will be fine.