Small Engines (Lawn Mowers, etc.): Is 90 drive belt same as 90 1/4?, transmission pulley, clutch pedal

Question
OEM calls for a 90 1/4" trans. drive belt for my craftsman/AYP mower but I could only get a 90" substitute--seems to be the only one offered now.  Will I need to adjust the pulley or anything--I laid the belts side by side and the new one is about an inch shorter (I assume the old one had stretched--plus it broke cause I caught the clutch pedal in a fence!).  Also, can I install the new belt with the deck on (by reaching sort of blind up over the deck and trying to fit it in place with help of mirror?)  Or do I have to remove deck again?  Any items to remove or get around?--I think I just loop one end around engine pulley and the other around rear transmission pulley and somewhere in middle fit flat end of belt against idler pulley--is that about right?   I have installed a deck blade belt several times.  Thanks so much in advance! PS this is mower model 917.25463 38"deck and I got trans belt #125907x

Answer
You will probably have to adjust the idler pulley like you suggested.  

You can put the trans belt on without removing the deck but is will be more difficult.  You will have to loop the belt over the back trans pulley and the engine pulley.  The gear shifter may have to be removed and there may be some belt guides to work around.

Did you purchase the belt from Sears?
Let me know.
Eric