Anyone using donut spares?

When I bought my 1972 Duster it only came with 4 wheels and tires, all 5x4 bolt pattern rally, and a B body 8-3/4 axle under the car... so two wheels didn’t fit... lol so fast forward a month now and I have bought enough parts to make a whole new car out of it, including what it takes to put power disc brakes on the front, which gets me to 5x4.5 all the way around. I am running 255/60R15 on 15x8 rims out back and 215/65R15 on 15x7 Zero offset rims up front once I convert to discs (tires are bought and mounted on new rims already). My car is equipped with Sure grip and I was told that if carry a spare match the rear tire height, which is 27.05”, The front tires are 25.99” and what I read is anything over 26” up front and you will have rubbing. So how do I do this spare thing right? I thought about it and these modern Mopars have donut spares in all kinds of sizes and a quick search yielded a great option, a 145/80R18 at 27.13”, definitely close enough for the rear height and narrow so maybe be ok up front with no rubbing? I mean the goal of the spare is to get the car home, and with it being a 340 car with 4.10 rear gears I am not going on any long hauls! Any opinions before I buy a donut?