1980 gulfstar CC prop size

[dbutts]

I purchased a 1980 gulfstar 44 CC. I took off the prop for inspection and found very bad electrolysis had deteriorated the prop. after taking it to the prop shop I found out that the 19x17 prop was the wrong prop, someone must have found a used prop that fit??
My question is what is the original prop size? Motor is a perkins 4.154 M with a borg warner 71 CR.
I found the specs for a gulfstar mk11 showing a prop size of 20 x 17 with a hurth 2.57:1 WOT is 3000 Rpm. Any help with my search would be appreciated.