Hi Peter,  I have Parker # 138 and the topsides is a paint. Long ago I asked Bill Parker and he referenced an Interlux #.  (I may have it in my notes somewhere.) ... Anyway.. I simply refinished with a similar color non-skid.....a couple nyears back, I refinished again..I used a more aqua color...you can see it if you reference my posts with changing to a larger engine by Martin Watson. 
Clean up surface with a good wash...sand if needed and be sure to use a tape that seals edges ..not simply masking tape..  I have used electricians black plastic tape (don't stretch it) ...now I found a product called Gator Tape that seals perfectly..no fuzzy lines.  Just follow the old paint lines.  
Marv Kowalewski
Parker #138 The Happyseal