22 year-old bike for the trainer

I just ordered a computrainer and am thinking about using it with my 22-year-old Cannondale road bike so I can ride outside without the hassle of swapping the tire, taking off the sensors, replacing the quick release, etc.  The bike is too small (it's a 54 and I ride a 56), but otherwise in decent shape.  I figure that if I can get the seat and handlebars in the right spot, it doesn't matter too much what size the frame is, and I can replicate my position.  I've found an adjustable stem for $22 that I think will work to bring the handlebars up to where I need them and far enough out front.  (My 35-year-old body has vastly differenty fitting preferences than when I bought the bike as a 13 year old--the top of the handlebars is 5" below the seat--arrgh.)  I wouldn't ride it on the road because I'm slightly above the minimum insertion line, but who cares on the trainer?

My biggest concern is the cranks.  They're 170 and my road bike has a 172.5.  Will I notice the difference? If I try to swap them out and can't find a 6/7 speed crankset, I'd need to swap out the derailleurs and shifters as well, wouldn't I?  And I think the rear hub is 126 rather than 130, so it wouldn't be worth it to put a newish crank on there just for the extra 2.5 mm if I had to replace the drivetrain.