Hey there, I’m here too!
I’ll try to cover all this, we are bound to miss something.
For ecu, control pack is easy. I have run mine on megasquirt, Holley, and a stock computer. I like the stock computer because of its driving manners, but Holley is probably the easiest to set up. If you get a stock ecu from the appropriate year mustang (needs to match the engine generation), then you have to send it out and get the pats deleted. You will also have to build the wiring harness that goes to a relay box for things such as injectors, coils, oxygen sensors, and so on.
Josef is spot on with the transmission stuff. I ran the t45 and it did just fine at 450 rwhp, shifting at 7800 rpm. I used to launch the car at 6-7k rpm on slicks. However, my transmission was built. I had everything I could inside that transmission except cryo treated gears and 26 spline input shaft. I’ve since gone to a 6r80 automatic.
K-member, yes I’ve got a BMR k member. I ran it with their control arms and later went to maximum Motorsports control arms. I really don’t have any complaints about their k member. They do have an option to use factory arms and perches to keep the coil springs.
Headers, you have options. I ran custom headers that I cobbled together from 2v headers and coyote flanges, then I had bbk, now I’ve got ultimate headers. Get whatever works in your budget. They all suck to install lol. But they all seem to do about the same. I made no different power going from 1-3/4 up to 1-7/8.
If I can steer you any one way, I’d say find a gen 1 truck engine. Preferably a 13-14 model, there were some changes to the cylinder heads. Mine made 436 rwhp with stock mustang cams, long tubes, and gen 3 intake manifold. In my opinion, the gen 1 engines idle better, and they are easier to tune. I later swapped mine to a gen 2 and I regret it.
Gen 2 engines have better connecting rods and cylinder heads, so if you buy one of those, swap in the gen 1 cams and use a gen 1 computer. So I guess I’d say get a 15-17 f150 engine, gen 1 mustang cams, and a gen 1 phaser/timing set.
Hope this all helps
