Get some flat cardboard pieces and tape them together to make one big piece that is a littel larger then the transom. From the inside of the boat push the cardboard into the area of the old transom. Trim the piece accordinly around the stringers etc...so it fits with a little room to play with. Presto you now have a template for the new transom. Getting the new transom in there may be a pain depending on how your stern is configured but very doable.
Strick
