I would say any engine selling at $1500 w/o exchange is junk. Dont have to look, or go to the link. The parts that a good engien requires will cost almost that alone, nevermind the machining, which I'm sure is not done with current equipment. There are no crate engine new unless its from Mopar performance, and those are of average quality. I'dsay you're looking at a 30-40% return rate witha MP crate motor. But there are plenty of places that can supply engines of similar make up..I call them "crate style" because they come complete, oil pan to intake, ready to bolt on a carb, exh, and install. Like the MP crate engines. Quality varies as much as the pricing, but if you see anything under about $4000, it's compromising stuff somewhere. Marine engines came in normal rotation (Clockwise) or reverse rotation (Counter Clock wise). Doesnt mean much until you try to run a CCW crank in a factory car setup, and the rear main starts leaking like mad, because the little oil grooves the factory cut are now pointing the wrong way. replace the crank, and you're ok. Size wise, I've never heard of larger than 440, but I'm no boat guy..They might have. I dont like marine cores, because a lot of them use the water they are in to cool the engine..If fresh, the block may be very rusty inside, and thin where you cant have it. There's a reason they tossed it out. If it's from salt water, it's junk anyway..same reason. A friend works at a marine shop, and in many instances, they just remove and toss the old ones..dont bother rebuilding, because the castings are so corroded inside. The items to look for in your search..Do they replace all worn parts? items like valve springs, valves, guides, main and head bolts, pushrods, rockers and shafts? What does the engine come with exactly? New fuel pump? water pump? the w/p housing? a factory intake? will they install a higher performance cam if it's not in there? What type of machines do they use to do the work? Stone valve jobs should be a thing of the past. Hardened exh seats should be installed to if it's billed as a street engine. Do they blueprint the block? Degree the cam? check rocker geometry? All rebuilts have new rings, bearings, core plugs, oil pump and screen, cam, timing set, stuff like that. But new and quality are not the same. You pay for nicer parts. Most places cringe if you ask these questions, they may say "thats a race only thing" or "our equipment is similar" or "there is no difference in what we use and the good stuff". The difference is in the lifespan, and the power produced. It's as simple as that. For a high performance rebuild with a little more power than stock, and much better running, I would say $3500 will do ya. I can do them for that easy with a core engine. For things like a better intake than stock, better pistons, and decent compression, a new oil pan, dipstick, valve covers, water pump, thermostat, and carb, it will run closer to $4500. I like to say, for under 400hp, figure $9/hp. For 400-450hp $10/hp for 450-500 $12/hp. for 500-550hp $15. Cores can be from $300-900 depending on needs.