hifi engine

Paisley Research Reference Two speakers

I've had a pair of these since new (1985?) and they both need woofer surround replacements but I don't know what repair kit to buy.
So my questions are:
1/ How do I measure the correct size of the woofer?
2/ Can I measure the size and then replace the surrounds without removing the woofer from the cabinet?
3/ I haven't been able to find anyone selling surrounds for Paisley speakers so do I just buy a generic surround to fit?

I'm fairly handy and have always enjoyed the performance of these units so want to do whatever I can to fix them.

Thanks for your help.