Wheel Vintiques Steel Wheels ?s

Frank, you understand right, what I call the spider is the center piece, and like said it can be placed Almost any where .
As to hoops IDK if they stock half sizes, I haven't talked to them since 2004.But they do custom work, for what I thought was very reasonable.

The rim sizes I suggested are minimums for the 85% rule I use. That is 85% of a 255tire is an 8.5 rim and 85% of a 235 tire is a 7.8 rim rounds either way, but on the front, fitting an 8 can be dicey, so I rounded down.
I round down for straightline work and up for cornering.

BTW
the profile numbers will change with any rim you select that is not 70% of branded size.
That is to say, a 275 tire is only a 275 when installed on a rim of 70% of the branded 275 size. So a 275 is 10.83 section and 70% of that is 7.6 inches, rounds down to 7.5. So in theory, if you mount a 275 on a 7.5 rim, you should get a section width of 275 or 10.83. In reality with rounding,your section width could be anywhere between 270.01 and 279.99, which all round to 275. This is a range of.39 inch.

but now, if you install that 275 on a 7.5 rim and run it at around 24psi in order to get the tread flat to the road, well, that's ok in straightline work. But as soon as you take a corner at say 30/35 mph, the chassis will roll over and pull up the inside edge,reducing your footprint, and if you're not careful, around you will go in a circle.
This is where my 85% rule comes in. 85% of 275 is a 9.2 rim, rounds to 9 inches. Now you will be able to run close to 30/32 psi , and the tire should remain flat to the road with all or most of it's tread gripping the road.
But what has happened to the section width?
Well it will grow more than 50% of the rimwidth change. so in this case 50% of 9.0 less 7.5=.75inch at least ,which is 19mm. So adding this 19 to the range of 270.01 to 279.99 gives us 289.01 to 298.99... which is still a .39 inch difference but now centered on 294mm or 11.6 inches +/- .2 inch. So yur 275 is now gonna be rounded to 295.
Normally this is no big deal, except when you have a limited amount of space in the wheelwell, like on a Dart,lol.

If I had a Dart, the very first thing I would do is move those stinking springs over, cuz 255s are friggin dangerous with anything over 300hp., worse with a shorter wheelbase Scamp (Edit; swb-car,lol). With 108wb cars, when the back lets go in the middle of a turn, you better be fast to catch it. In a Dart you might have a couple of milliseconds more time,lol.
And the second thing I would do is figure out how to install 275s in or under, and somewhere close to just barely not rubbing on the inner sides of the tub. This will vary with the arch of your springs, the flexibility of your bushings, the height of your shackles, the compliance of your shocks AND most importantly ; how hot you're coming in. One half inch is said to be adequate, I have run less with poly bushings, nearly flat springs, HD shocks, and not getting crazy on the gas (430 hp).