Look into Marine Power in Ponchatoula, LA. They provide GM based marinized engines and gears. I don't remember the company name to look under to be able to buy direct, but I suggest you call Tyler Baker and he could help you.
1983 Present 42 Sundeck
Twin Lehman 135's
Steve Point Cadet/ Biloxi, Mississippi USA
*Present 42 twin 135 Lehmans