All things being equal, I'd consider the 4.236 vs larger 6 cylinder a huge plus. In my opinion, the 4.236 is the best engine Perkins made. Parts are reasonable, reliable, and long lived. My single 4.236 pushes my displacement hull along at 6.7 kts at 1700 rpm and burns around 1.2 gph. A pair in your boat should run around 2. 5 gph combined and run 7 kts.
I'm not a twin guy, but if I was, twin 4.236s would get my attention.
1970 Willard 36 Sedan Trawler
Current Location: Ensenada MX