It's a gamble if you try to guess what is in there. There could have been changes made over the past 50+ years.
And, as you probably know, 10" or 11" were original equipment sizes.
I always take mine out and take the assembly into the parts store - if they are willing/interested in measuring/matching what I have.
Otherwise, I measure the distance between opposite-sides pressure-plate mounting holes and get a complete assembly that bolts up to those holes.
