Wait until your motor comes in and take it to the pawn shop with you to test fit it.
The angle of the seat post will determine how level your carb will sit so check it.
Chances are you will need a different front mount that will fit around the usually fatter front tube.
http://SickBikeParts.com has them but you need to ACCURATELY measure the diameter of it to order the right one.
When looking the bike check the brakes and also the back wheel.
Grab the frame with one hand and try pushing the back wheel side to side. If it moves forget it, then spin it, if it isn't true or has loose spokes forget it.
The hardest thing for a rookie to get right is the rear sprocket, if the rear wheel isn't perfect to start with you are just wasting time and money as a couple of HP will rip the thing to shreds.
One other note is don't buy a Huffy, they are crap new and don't get better used.