If you're not needing or wanting a vintage, in period engine................OPTION #4!
If with no concern for truly "old stuff" of the period, buy "new stuff" for better durability and big horsepower intentions, it'll be cheaper in the end. 
Scott.
Wanna buy it? Ha. I’ve been looking for a good 427 block for a while, kinda hard to find. I do like the idea of a Ford block in my Fairlane.
NA, ...... probably have eight or ten (?) including even "new-in-the-box" still left over waiting for builds. We quit buying them a long time ago, decided it is better to let the customers find and invest in something, bring it to us, and then I'm not at a loss when it turns out to be junk! Which happens all to often these days with this stuff.
And again, if one wants a "period" engine in their '66 Fairlane, then certainly build it! And if so, (remember you asked!) then OPTION #1, with perhaps an end result of a performance level of something greater than the original, but just don't try and be to crazy in the effort (OPTION # 2 & #3) and just waste what might be an example of an ever dwindling supply of "good" originals.
I guess I just disapprove of wasting something for naught (including ones' budget), as if pushed, the old originals just aren't that tough, and if your going for OPTION #2 and/or #3 with vigor, its' not going to be anything like an original, so why worry about the presents or not of FOMOCO being cast in the otherwise weak block for the potential power level intention?
Scott.
P.S. Oh, and I already have a '67 "R" code Fairlane w/ the 427M.R.; and we raced (street & track) a '70 Shelby GT500 with a 461 cu. in. Tunnel-Port, and that's enough.
And if you wish assistance with your effort we are very capable in the arena of the Ford FE's (for example we currently have two 390's +/-, two 428's, & three 427's of customer builds in the shop now and it ain't like these are first ones we ever saw!).
Scott.
