I put all the original parts back, and it still didn't fit - taht's what
baffles me - any clues?   oh, and I miked the tensioning roller and the new
one is about .010 larger - about what I'd expect for wear, so I don't think
it's the roller - I don't see any way I could assemble this thing
incorrectly - and moreover I've changed belts on 944s before - this is just
baffling, but something must be interacting with the belt layout - darned if
I can figure out what.....

Could one of the rollers be larger than the one removed by a slight margin?

following up on this - I tried putting the original belt and original
tensioning roller back, the and had the same problem - not long enough -
WTF???   so, I took the tensioner assembly to my mill and enlongated the
slot so it could retract another 3/16 or so - that helped, but still not
long enough - I didn't have to fight to get the belt off when I removed it
to change the seals - what the heck could have happened ?  I'd really like
to get this to where the tensioner actually is not on the stop.

oh, by the way, the "S" cars use a wider and longer timing belt than the
non-S cars, and a different tensioning roller.

any suggestions, anyone??

been channging the front seals on a 944S (seemed like a good idea), got all
new rollers too (also seemed like a good idea), and decided to change the
belts while it was all appart (yep, seemed like a good idea) - I've done
this before, its usually easy to put the belt on  - relive the tension, put
the belt on, release the tensioner (or if early car, apply proper tension)
and you are done - well not this time - it took me over an hour to get the
belt on, finally I got it on by rotating the engine by putting a wrench on
the cam shaft and pulling it onto the gears - it's now on, the car is
properly timed, and it runs - but ----- the tensioner (this is an 87) is
held hard against the stop by the belt tension - I don't hear that tell-tale
whine, so belt is not too extremely overtinght, but it bothers me that the
tensioner doesn't even come off the stops one iota - I suppose the belt is
just a MM or two too short, though the teeth fit in the slots on the gears
correctly - could there be any other cause that I should look for?  I don't
really want to break a belt on a 16V car, but then again ....