Help fix my compressor?

So yesterday, out of frustration, I impulse bought a 3 gallon compressor from HF, thinking it would be like my old 4 gallon. I neglected the motor difference, and the 1/3HP motor on the HF compressor is useless. this may seem irrelevant now, but it's important for later.

So I dug out my old compressor. Some fairgrounds toolsale we picked it up for $100 and it was great for years until the regulator got snapped off in storage. After going through the most obnoxious tear down procedure I've come across, I replaced the regulator, and forgot teflon tape. Needless to say it leaked and got shoved back in the garage for future me to deal with.

Well future me is now present me. In essence, I have 2 compressors, a 2HP 4.4 gallon that needs fixed. I tore it down again today, teflon on all the joints, and it seems to work, except this part broke. The tube feels like potmetal to me. There is a compression fitting attached by the gauge, which I assume this is the pressure switch line, the end that broke was flared to fit that nut currently attached. This is what's behind the nut.

Can I replace this with brake line or maybe copper tubing and be fine?

I did this with some JB weld, because screw it I gotta replace the line anyway. I haven't tested it yet, but since it seals the gap and leave the pipe open I think it might work. Maybe.

This brings me to plan B, and the HF compressor. Is there some way I can set things up to have 7.4 gallons of air from one motor and set of lines? Basically use the HF tank as a spare tank and get rid of the motor?

This is the HF compressor. The air goes into the tank through the rubber hose, in the top right is the pressure switch, shuts off at 100psi on at 80 PSI, and at the bottom center, is the regulator and output that I'd ideally like to use.

I guess I screwed up, but the part where the air comes out of the motor is at the back, it's a 90 pointing down that goes into that half inch tubing that goes to the T where the line that's broken is. Instead of going into and using the twin tanks, I just want to connect it to the HF 3 gallon single tank. I just don't know what to look for or how to go about making it work.

Even if there is a fitting or adapter or something I could make to go from the output of the 2HP motor to the 3 gallon tank and get rid of the 4.4 gallon twin tank setup, that would help. Even better would be a bigger tank overall, but I haven't gone looking for a compressor with a dead motor yet.

TL;DR Can I use brakeline or fuel line for the piece that goes to the switch on my compressor, if not, can I hook the tanks up to work together, or swap motors easily?

Brake line, fuel line, copper line, compression fittings, bubble gum, use whatever will seal/hold air.

The easy way to get capacity is a quick connect fitting on whichever tank you pull the motor from, then just toss a hose to it from the other one and hook your tool hose to the outlet of the motorless tank.

We have a semi truck air brake tank with air fittings for extra capacity on multi nailer jobs like roofing where the pancake compressor would otherwise just run all day

For repair on that line anything is going to work. Rubber air hose, copper, steel, whatever. Most of the lines on my compressors from the little jobsite pancake to the 60 gallon garage one are copper

Well, I snagged a chunk of brake line today. The flared end fits fine. With lots of precision bending, I managed to get the compression end to where it needs to be. With the old compression fitting, some weird cone on shaft design, it wanted to cross thread. I bought a new compression sleeve and nut, and they fit perfectly, but don't seal.

grumbles

The remaining misc air compressor bits and pieces I have are all too big to easily fit on the small compressor body.

I think I've figured out how to wire up the small compressors air switch to the big motor, but without a way to connect the motor to the tank, that's pretty pointless.

Guess buying a new big compressor is now a priority, so I can get the vic back on the road and the miata up in the air.

Fixed the compressor with fuel line, still can't get the bolt out though. I have spares, thankfully, so I guess it's sawzall time.

All this work and money to do what I originally could have done.