CB,
I have a fully inflated coker 185 redline on a stock steel rim as my spare in my 73 TR6. It is a tight fit, but it does fit. Factory specified the same size tire as this as well so not sure why it wouldn't fit otherwise.
As another option, some guys have gone with a space saver spare successfully. Check Bobby D's site for more info on where to find one.
Cheers,
Tush