OK You asked...We have a 34C Silverton with twin 454's. Our boat is a bit lighter than the AFT CABIN you are looking at. At typical cruise speeds we burn about 28-30 gallons an hour with OUR setup. AT WOT we can burn 44-46 gallons an hour and obviously we don't do that much. Personally, I think the Crusader is about the best gasoline engines for marine use. Maintenance for US has been minimal but we do much preventitive maintenance. Our Silverton is a solid boat that does well in 4-6 ft seas... more than I do. As for hours, some members here have run over 2000 hours and more but obvioulsy previous maintenance and use will dictate longevity. My 2001 F-150 is rounding 290,000 miles BUT I do take care of its maintenance and use.
This website you are at will be your absolute best friend with your Crusader engines. While you are at it, check out the Silvertonclub forums for well detailed information on specific models and opinions.