Booster problem? Pedal doesn't return.

[Spyder]

I really want to take this thing for its first drive and sest the rings.

Brake pedal isnt returning past about halfway. Bottom half of the throw it feels fine but the top half it swings free after a partial return.

It sits low enough without pressure the brake lights come on. I bled them and got air out, no change in pedal feel. I'm guessing I messed up the booster when I had it off to paint the engine bay Bidy color. I don't mind just replacing it if that's the easiest, but all the ones I'm seeing are different than this lower profile one and none are low cost.

Ideas to check or try before I replace it, and if I replace it with the bigger version I'm seeing available will that work?

Car is a factory disc power brake car.
Here's what's in it now. Worked fine before the engine came out so I assume I broke it, put it together wrong, or missed putting something in that should be there.

 

[Challenger RTA]

Just has some bake problem on an other car of mine. Did the same thing as yours. Right a way I was going to change the booster and master cylinder. Diagnose first. Is the booster holding vacuum? When at idle can you pull the vacuum hose off the booster and is there vac? Check the check valve see it it is working. Has vac and holding vac. Master cylinder working Does it pump up and can you bleed any fluid out? I could bleed mine but it was only a 50% steam as usual. Is the fluid clean? Even with fresh fluid it was the same. Mine was a little dark. Ended up the line where flushed from the constant bleeding. When moving car very slowly will it stop when using the brakes. Yes mine did but it was not full pedal. Pedal would kind of pump up but when done only about half way up when done.
Ended up finding a rear wheel cylinder was not working. Replaced it and all is good.

 

[Xcudame]

Definitely check every where for leaks! Including the brake booster (fluid and vacuum)! And make sure all the lines are bled really well once no leaks are evident.