Mike,

I hate to say this now after you are well into the project, but the idea of restoring a Perkins 4-107 is not a very good idea.  The technology is far too old.  The 4-108 is pretty much a different engine, and I doubt if any of the basic engine parts would work on the 4-107.  The alternator, and possibly the starter would work, but I doubt if the high pressure fuel pump or water pumps, etc., would work.

You could probably use the 4-108 as is, since it will fit in a W32, depending on it's running condition.  However, I would not recommend trying to do a complete rebuild of the 4-108, as it also is very old technology, and parts are getting harder to come by, and expensive.

These are early 1970 to mid 1980 engines.  Are you still using your 30 year old mid 1980 car ?  And what did that 1980 car cost new, compared with what a new car costs today.  Maybe better to just bite the bullet, and get a new engine.

Just my humble opinion, for what it's worth.