JammedStab
Sorry for the delay - have been a bit busy last couple of weeks.
AFAIK - the -28 had an uprated compressor with more airflow - an uprated hot section - and was operated with more torque than the -27. Also I seem to remember that the compressor bleed valves were also different. Part of the upgrade was for higher altitude performance but also for increased airflow for bleed air used for heating and pressurization purposes. I don't have access to anyone at Pratt that is in the know any more so this is the best I can do. Hopefully it is enough or someone who has more experience with the engine than I do can explain further.
As for the P&W 100 series engine - I have a pile of stuff for it - from Dash 8 - EMB Brazzie - D328 etc. but the problem is that it is still a production engine and probably more important all the training materials I have developed were for specific companies and as such are subject to copy-write issues. Thus it is not easy to just dump them onto the internet - even for free!! Some companies like "Flight Safety" are fully aware of how much of their stuff gets ripped off and until you have actually had to sit in front of a computer for years producing manuals and training material you have no idea as to how much work - and money - it takes to do this. Now if someone wants to hire me to do a set of free manuals I come pretty reasonable but I think you would be very surprised at the end cost.
A small aircraft course - say something like the Beech 1900D - will cost in the neighborhood of about $35,000.00 Cdn. to have produced by someone like me. If I was to see that material offered for sale on the internet or even given away for free; as the owner of the material I would be a little more than upset.
On that note - if I can find a set of very old training documents in my archive I might be able to make a P&W 100 manual into a digital file without a lot of work. But it is going to depend on where the source material came from. If I can use it without copy-right infringement then I will put it up for everyone.
Hope this answers a couple of your questions.