The Powermatic 26/27 were fine machines for light duty shaping. I personally think the 5 hp motor and 1-1/4" spindle on these machines was due to marketing and optimism as the machine isn't really robust enough to handle them fully.
This is a Powermatic bearing….the one sitting inside the Martin bearing that is!
http://i762.photobucket.com/albums/x...g/bearing2.jpg
You can see one of these can handle the demands made on a 1-1/4" spindle and the other….not quite so much. I'm one of the guys who was overly optimistic with his 27 as Jack eluded to. I used to run a 4" corrugated head on occasion. Bearings lasted just over a year. All this to say that just swapping in a bigger spindle and/or motor does not make the machine more capable. All depends on what you have for bearings and quill assembly.
good luck,
JeffD