Ima thinking that adapters on the front is a bad idea. Especially so if you have the 9" front drums with the tiny wheelbearings. Those adapters are gonna put a lotta stress on the tiny outboard wheel-bearing. Plus, if you offset the wheels to the outside, this will increase your scrub radius , and that is gonna negatively impact your alignment. The usual result is a pull, and or wandering, and/or premature death of the tire treads.
On the front, you need to maintain the scrub radius.
Which means, that as the tire gets taller, it has to be brought inboard.
Ima thinking that a 245 would look really good in there, on an 8"rim. I'd get a custom wheel with a matching pattern to the current bolt pattern, no adapters. And I would go heavy on the backspace, and have a couple of hub-spacers on hand to fine tune the scrub radius. This may require longer wheel studs.
An 8" steel wheel actually measure 9 inches outside to outside, and so, a 4.5"backspace puts the mounting flange right in the center. However, that much backspace may put the wheel into the upper BJ at full droop. And, as the tire gets taller, the Scrub radius is moving outboard. So sooner or later, your car is gonna get nervous in straight-line driving.
So, if you intend to do a lotta hiway driving, I doubt you will be able to utilize an 8" wheel.
Thus, in your case, I suggest a 7" wheel with an inboard offset to the max, just before it hits the BJ, again 4.5 is likely a hair too much, so order spacers. This will position your scrub-radius better with a taller tire.
A 7" wheel will accept a tire in the range of 205>215, but in a 75 series might accept maybe a 225, which will be about 28 inches tall..
A 5.5 wheel will accept a 5.5 tread easily enough, which might have a 7" profile, which maths to 175mm. This will not get you much more than about 25.9 tall on a 15. For example, say you went 185/75-15, which could be ~25.9. You would have to experiment with tire pressure to get that tire to run flat on the road for a long tread life. On a standard-issue zero offset wheel, it's gonna wander at hiway speed. and, it may have the occasional pull around town, on less than dead-flat roads like well-worn asphalts. On concrete, it might be alright.
Just a reminder, if you run a bolt-pattern adapter on the front, this adds 1 inch to the offset, which has to be compensated for by a custom wheel, else you will have the mentioned alignment problems. and with a taller tire, the scrub radius will end up giving you steering quirks. I highly recommend not to do it. Especially if you have 9" brakes in the which that outer bearing is gonna take a chit-kicking. I have personally broken two of those spindles off with just stock wheels. When the spindle breaks, the wheel comes off with the drum , the car falls down and the wheel keeps going, usually wrecking the wheel house. and of course, you got no front brakes, which doesn't really matter, cuz the backing plate is digging a rut in the asphalt, until the car stops. If this happens in traffic, that runaway wheel is likely gonna do other damage to other cars.
