First, get hold of mike and check his production schedule for AL heads. Not sure whats in stock. I knew there were some supply issues, but not sure if they've been addressed yet or not.
I would consider going straight to the 4V. Manifold price I believe is the same and you can get a second hand Holley 4V for $200 or less if you look around. And that's usually in decent running condition.
Gears look like a good combination, though it'll depend on the T5 you get. If you get a 4 cylinder T5, 3.55 will be just a bit on the high side. A 3.20 or 3.40 I think would be better. I ran both with a 4 cylinder T5, and with the 3.40 is a tad bit high. I mean, for highway it's nice, but around town, 1st gear was about useless. Many times I just started in 2nd. with the 3.20, it was a nice combination. With a V-8 T5, a 3.55 is a great number, maybe even a 3.80. I'm still running the 3.40 with my V8 T5 I have now, and it's a tad low. Engine doesn't like 5th gear for cruising until I'm over 55. On the nice side, 1st-4th is really fun on the back roads.
Personally, I don't like solid cams. I'd go with one of Mike's hydraulic cames, like the dual 274 if you want a little more umph and don't mind some loopiness. I don't like the engine to chop too much, so I went with a comp cam 260H (before mike carried cams). Basically, what you get out of the cam over the stock is about 30% more lift, which is the real performance gainer. With AC though, might want to make sure the 274 isn't too much, but I think it hsould be fine. I will qualify that statement with the fact that I am NOT a cam expert.
More rocker ratio...more lift...more air. Just make sure you check your piston to valve clearance.
For springs, I strongly recommend the NPD 480# springs. They are not too harsh in a 6 cylinder, especially if you want to grip some corners. Combine them with some Edelbrock Performer IAS shocks, and I think you'll be as happy as I am. I also am running mid-eye rear leaf springs from Mustang Depot. (Grab-a-trak). Very nice rear springs. Car handles very well on the twisties, but isn't harsh on rough roads. Until a few years ago, was driving the car around 5k miles a year with this set up and still love it.
