with Williams games I always check , ipdb.org.. sometimes they are shared (never for gottliebs) fortunately, there is a schematic for your skill pool. I had to buy mine for my gottlieb skill pool but was rather surprised to get an original copy from pbr a year or so ago ..rather than a .. copied version ..
anyways.. take a look here
http://ipdb.org/search.pl?any=skill+pool&search=Search+Database&searchtype=quick#2182