Re: Westerbeke - no start post inj. pump rebuild.
How about a little history on the engine. Why did you get the pump and injectors rebuilt were there any other running problems when it last ran or any other evidence for us to help you diagnose your problem?
As John said, timing if it can be set is the first thing that comes to mind. Compression would be next but, you mentioned slow cranking speed. Engine rpm during cranking should be approximately 250 rpm if it is significantly slower you need to find out why. It shouldn't be hard to believe that compression would drop to the point of being hard to start or needing a starting aid to help get her going it's 32 years old that's pretty damn old for an engine especially if it is original and slow cranking along with.
Diesel fuel autoignition temp is approximately 600 deg yours may depending on which grade fuel you have but your compression would have to be above 300 psi for autoignition (that's actually pretty low). Cylinder temperature rises 2 deg for every 1 psi of compression. So, slow crank speed and/or low compression will will not generate enough heat during the compression stroke and cause an engine to be very hard to start.
Always check the easy stuff first and NEVER assume. Gather more evidence.