<VV> spare tire question

[John McMahon]

Hi,

I've got a 1965 Monza that's almost ready to come down off the jack stands. 
I'm putting 15" wheels on it and tires with a diameter of about 25".  I 
would like to use one of my 13" wheels for a spare, but the largest tire I 
can find for it is about 23".  This car has positraction, and someone in the 
archives says that using a "donut" spare with such a setup can ruin the 
posi.  Now a 23" tire is not a "donut" tire, but it is a significant 
difference.  Would this be a problem?

Thanks,

John McMahon
1965 Monza coupe 110 with posi