The 45 has Detroit 6V92TAs, Covington conversions, with twin dry turbos. They scream like a banshee (4 turbos down there will do that!) but the boat's great and those engines, properly taken care of, are fantastic. I love 'em even if they do leak a bit of oil and aren't as "social", and are more thirsty, than their "modern" counterparts.
I carry 500 gals of usable fuel, and burn about 2gpm at cruise (18ish knots), for a working range of 200nm, plus at least 50nm of safety reserve. In reality I probably have "thirds" on the reserve, but I don't play close to the line on that - running out of fuel in a 25 ton boat is not a good thing.
Transoms are a real PITA to replace.
Those kinds of shortcuts ARE the norm with MOST builders. There are exceptions though. One of the problems is that even the best manufacturers (e.g. Hatteras, Bertram, etc) have built some stinkers, so you have to know what to look for BEFORE you buy, lest you wind up with trouble.
If/when you redo that transom let me know as I can give you a few tips. Any time you replace structural wood in a boat, coat it on all sides, and especially the end grains, with epoxy. You will not have rot problems if you do that.