I purchased the landing gear from Ziroli. It's made by Robart and cost $525.00.  Ouch!

It's not particularly hard to install the gear, it's just a lot of mark, cut, test, mark, cut, test etc.

I used a Schrader type fill valve (like a bicycle tube valve) from Sierra Precision. This makes filling the two air tanks much faster as you can actually use a bicycle pump.

This photo shows the fill valve, a pounds per square inch (psi) air gauge also made by Sierra Precision and the retract valve. The regular Robart air valve did not move enough air to cycle the big retracts.  The Sierra valve has a larger piston diameter and longer stroke and does the job perfectly.

This is how I tested the retracts. I made foam stands so I could get a complete retract cycle. Be sure to balance the P-38 with the gear up!  The center of gravity moves aft with the gear up.