I don't see a problem, all it means is the idler pulley will come out just a little further. Thats the piece that puts tension on the belt anyway.
Ya, but you are allready starting out with a "stretched" belt....Why???
FYI: I bought a "NAPA" belt for my snake (too lazy to drive to a dealer) and it started slipping after just a few miles....Bought a "Mopar" belt....no problems so far...
Cheers,
Sounds like there was more to it. The belt tensioner (if the spring is up the spec) will more than compensate for 3/10th's. A good quality rubber belt doesn't require a great deal of pressure. One that has been sitting on the self for lord knows how long will be dry and not have much adhesion on your pulleys. So I would say that if we are talking within 3/10's that the quality of the belt would be a bigger factor when you are using a tensioner pulley that has likely close to an inch of travel. BTW these belts are line with nylon etc.. so that the stretching is limited.
Don't get me wrong, I'm not saying that an aftermarket belt is the way to go, but I wouldn't be concerned about one that is a c^*t hair longer than the stock belt.