I thought the 4 speed prop shaft had UJ's (and only the 5 speed had CV joints)? If it has CV joints I have heard that Mini CV boots fit but I am not sure how they are fitted. I have a spare prop shaft which needs new gaiters and some Mini boots but have never got around to trying to fit them.
If it has gaiters it is probably better to replace the prop shaft with one with UJ's (available from several specialists) as they last better and can be fitted with nipples for lubrication, and rebuilt if necessary.
Saab 9-5 2.3t Vector Auto Estate Stage 1
Saab 9-3 2.0 SE Turbo Convertible
'81 TR7 DHC