Spare tire, space saver donut options?

I converted my 68 cuda to 4.5 B.P. Of course it has the wheel well in the trunk floor. Keeping it all Mopar, I got a never used spare donut from a Jeep Cherokee or Grand Cherokee from a bone yard for $10-15 and the trunk panel fits very nicely without being too high. I'm sure I tried it on my front 73 disc brakes and it fut ir it wouldn't be in the well. Luckily I never had to use it yet.
I consider it for emergency use only and would have no qualms about using it with my S.G. for short distances less than say, 50 mph.