Cores need a rebuild and drop in engines run and won't need a rebuild. Here are a few for you to check out in your area. How many miles does Layla have on her now>????? Keep in mind 300 I6 Core engines are dime a dozen in old beater trucks. you should be able to find a old truck with engine or just a core for $200-$500 really easy! I like the first link below the best unless you want a parts truck... You can use that rebuilt block and turn it into a long block with rotating assembly with head. You'll probably need a seals and gasket kit for $100 and a few things from your engine but it would be the cheapest way to get a zero mile I6 into Layla!
Already rebuilt and needs assembly (good deal!):
300 Ford 6
300 Ford Industrial Engine
1985 Ford F-150 4x4
1990 ford f150 parting out
1988 ford bronco
Drop in replacement engine.
1995 F150 4.9L 300 inline six motors
92' E150 van $650.00 OBO parting or all
Keep in mind if you find one that is running and sounds good. Chances are you're not going to have problems rebuilding it and using it as a core. That's why I'll buy a parts truck for $500 or less if i can drive it away or hear it run. You know the engine is good at that point and the rest of the truck can be hauled to the metal recyclers to recoop some $$$$!