[elmariachi]

Realizing that none of us really answered your questions:

If you read around these forums, you'll find names like Keith Craft, Barry Rabotnick and and George Anderson, all of whom build LOTS of Cobra engines. They build turn-key engines but also sell parts and if you are polite, will generally offer very sage advice because they don't want to see anyone in this sport make a mistake or waste money. After a few phone calls and lots of reading, you'll get a thorough sense of what each engine will cost you to buy and or build, and which one might be best for you. Those guys are a great source for reliable and hard-to-find parts.

I am less than a year with my FE-powered Cobra, but here is what I have learned, with regard to your specific questions:

1) Is it worth the cost going for a 427 block, and what would my choices be (e.g. Original, Genesis block with 1966 stamp etc.)? You must decide how important it is to you to have an FE powerplant. Abstract feelings like nostalgia, ego and bragging rights become monetized very quickly with an FE, especially a virgin side oiler. There are a decent supply of original used blocks out there, a few NOS blocks and the Pond and Genesis. The guys mentioned above generally have access to all of them. Search for Pond and Genesis here on CC and read about the pros and CONS.

2) Do I need to worry about TO vs. SO for street use? No.

3) Is the 428 just as good for street use as the 427? Yes.

4) what kind of cost should I expect to pay for the different (original) blocks, 427SO, 427 TO and 428 respectively. Impossible to say, as prices and availability change with the wind. Just start calling around and taking notes and you'll start to get an idea.

5) what specific things outside over bore should I look out for if I buy an original block? There are battery of tests (sonic, core shift, porosity, mag) that should be run on any old, used block (or even NOS in the crate for that matter.) Failure to have these tests conducted could cost you thousands within minutes of first start. You think the High Command has been a tough sell thus far, wait 'til your new baby pukes its forged/domed/ported/balanced guts up on your garage floor.

6) are any of these blocks compatible with / have provisions for aftermarket A/C systems? I have heard it done, but AC in a roadster without a top is sorta like a heater on a snowmobile, no?

7) I have also talked to some people who have urged me not to go the FE route and get a 351 sportsman or 351 BOSS block instead, and then if need be bore / stroke it to 427. There are lots of great reasons to go with a 351-based engine. I just spent 8 months and lots of $$ gathering all the parts to build a mild, date-code correct 450HP side oiler. Its neat, but there are plenty of small blocks out there that can blow me away. Guess its all a matter of your priorities.