The original prop was a 13 x 13 unless it was a 3 event promo boat, then it was a 13 x 12 (first # is diameter, second # pitch)
You need to determine your actual full throttle RPM then go from there in selection, first guess is a 13 x 12 sand cast type 3 blade, if your buying a cnc machined prop it may be a 13 x 11