When I switched, I used a Ford A351 block, but there are higher and lower priced options out there. An old seasoned block will do, almost no matter what year. I also chose to go with a solid roller cam, though most may recommend hydraulic. A good forged rotating assembly is a must and I just saw a new in box set up sell for $1,800. Headers will possibly be your biggest concern once the engine is together. I'm thinking
KOOKS myself, because I didn't use them and had too many clearance issues. Then again, if you just go with 1 3/4" primaries, you'll probably be fine. Get solid mounts and something like a Flaming River rack if you plan to use manual steering. It's worth the money imo. 1st thing though, PREPARE the chassis! The stock chassis will just be annihilated by a strong 408. Stiffen things up with sub-frames and if you can stand it, a roll bar or cage.
Build the rear well, tossing C-clip stuff completely and using at least 31 spline axles. And don't forget cooling. Upgrade the rad with whatever you like best, aluminum or a 2core brass unit. For daily use, I like brass.
205's will be good imo. It's just a matter of how much you wanna spend for the performance. Also, the Spyder intake seems to be great, but maybe there are better units these days. For your electronics, there are many choices and I'd recommend spending time to look into various brands. The best for you may not be the most or least expensive as I'm sure you know. I went with a carb because it was less expensive. Looking back, I would be kicking myself if I felt I could afford injection. It's cleaner, easier to manage and I think overall, easier to work with because adjustments are minimal compared to a carb and start up is also easier.
Final thought... Pay CLOSE attention to which transmission you use. A T-5 won't handle the torque or power. If you want manual, I'd say 6speed for sure. For an auto, it's gotta be built well and all are likely to be a tight, heavy fit. I've used a 4spd and a C4, then switched to C6 because the others just weren't ready no matter what I did. 408 is a great choice as far as I can tell. Most of all, have FUN with the build. If ya get mad about it, walk away and come back later. You'll remember the experience with more smiles.