About the only think you will have problems with on the Puch is the Speedo. They are real clunkers, and I have seen MANY go out. Keep the cable and speedo. drive lubed with graphite.
Change the tranny fluid with TYpe F Auto Transmission Fluid. Its probably been sitting in there for a long time. 5.4 oz, or till it comes out of the hole on level ground. If you have trouble getting the bolt out... tap it with a rubber hammer lightly, put the bike down on it's side gently, and use a straight edge longways ( a standard screw driver works great, used on it's side) to loosen the bolt.
Hmm.. other things... ( trying to think of what my 78 needed...)
Ah yes, if it has been sitting for a REAL long time, you may need to replace the float needle in the carb. The rubber tends to dry out and shrink, cuasing the jet to stay open all time, filling the bowl up until it overflows. Real easy job... takes about 5 minutes. I can get you diagrams and pictures from a repair manual if you need them, but it's a good idea to get the manuals from the Moped Warehouse.