I'm kind of curious about why you think the length of pull is off. I assume
you mean it is too long. You could get a ladies or boys model shotgun to try to get one with a shorter length of pull. You might want to broaden your options. Unless you plan on using the gun for other things two shots is more than enough. Heck, the times I've gotten off a second shot at a turkey it's been a waste of time. Unless again, you are using it for some other sport that involves pass shooting, if you can shoulder the gun and fire it reasonably well I don't think length of pull is that important here. When you hear a turkey coming you should already have the gun up and pointed in the direction you anticipate him. If you wait to throw the gun up, more than likely he'll see you do it and leave.
As to 3.5's: there are two schools of thought on shot size. One is to use small shot and aim at the head, the other is to use large shot and aim at the neck and body. If recoil is a problem you might think about using small shot and aiming at the head. You can use a reduced load and you will not be able to shoot as far but you'll throw more pellets.