Rob, first firgure a good 428 block will run around $400-800 depending on if it's a std 428 or CJ block. This is just for the block. This is also going by DSC's pricing and you might do better and come across something though. A 390 might be a better alternative cash wise and you can put a 428 crank in it to make a 410. Port the heads and get a nice cam, intake and carb and rebuild it and you should have a nice 390. This is way cheaper than a 428 and for the most part just as good and 400 HP is very doable. Early FE blocks (64 and earlier) have 2 bolt motor mounts and the 65 and later the 4 bolt. You can easily convert later mounts to fit an early block if needed. You can also use steel shim head gaskets to bump the comp ratio up a bit if needed before milling the heads. DSC sells them for 390's and 428/427's for $30 a set. Toploaders can be found in good condition fairly cheap but take Richards warning as well advised. A 5sp Tremec conversion is also a nice option as well and can be done easily. Either way it sounds like things are moving along nicely for you. Take your time and look at a few different engines and compare what they have vs the price. Most FE engines have been rebuilt a few times and some have a interesting assortment of parts. The casting numbers will tell most of the story as far as what parts are in the engines you look at. Most guy's will have no problem taking a head off or the oil pan for you to inspect the bore and internals. The ones who won't might have something to hide so be careful. Good luck and let us know how you make out.

Glenn.