My FFR build is still a few years out however I have a 97 Mustang in need of an engine now and plan on it being the donor for the build long term. What I will want in the FFR build is a good street-able engine.
So I find myself in a fix as the engine decision keeps evading me. An earlier 302 engine with carb would greatly reduce the complexity of the wiring and eliminate the ECU issues. But a carb tune is only right for one temperature and air density setting. I have a high comfort level with the basic configuration of the 302 and like the torque properties. Likewise a 302 from a 94-95 Mustang could be used with its original Fuel Injection and computer. Main disadvantage of this setup its too ugly to open the hood. Also a 302 with manifold change and one of the add-on EFI setups could be used. The advantages of that are the throwback look of carb engine for period feel with the advantages of Fuel Injection adjusting to the conditions. So that's 3 variations all on the old Windsor small block.
Then there seems to be a current trend toward using the Coyote. There is a lot right with going this way. Great power and drivable, but it has many mechanical and electrical parts with which I have no experience. Also the power is way above what the stock T-5 can handle. And maybe more of a concern to me I don't believe you can get all that power hooked up in a chassis as light as the FFR kits. I really don't need something that can melt the tires. This is likely tempered with my daily driver, a 2011 Mustang V-6 Convertible that was the first year for the 305HP V-6 (looks to me to be 3/4 of a Coyote). That car weighs in around 4000 with me and a full tank and is plenty capable of doing more than I ask in terms of acceleration. Also gets 21 mpg tooling around town.
So for me I would be happy if I could put a 3.7 V-6 like my daily in a FFR kit. I think it might have the perfect balance of power and weight however there's no Ford Racing Control pack to aid moving this engine out of the Mustangs. Perhaps its just my lack of current tech that I am unaware how that might be done. If anyone has ideas I would sure like to hear them?
There is nothing wrong with using a vintage 302 or the new Coyote but I would love to be the first to put a modern V-6 in there, after all it was good enough for the new Ford GT.