I have an Imbel receiver FAL built by Enterprise about 10 yeas ago. The barrel is Imbel 21 with a mixture of Austrian and American parts
The Austrian kit was from DSA and reparked by them.
What is the going price?  A friend of mine wants it. I don't know how
Much I should ask.  It was but during the ban era, so it has a pinned muzzle break.
350 rounds threw it.
"This is not an offer to sell."

By Austrian I assume you mean STG 58. It really depends on if the kit is matching with lower. Gunthings is selling a non matching set for $900. You cannot find STG 58 kit anymore. So  your Stg parts can go for 8-900. An Imbel receiver goes for about 500. That is your baseline and you can add, subtract, depending on condition of gun and your friendship. Completed gun market is soft now. Parts sell for more. My 2 cents

Entreprise is selling Imbel kits for $299 and up.  Reparked is $425

I paid $125 for the STG 58 Kit and $175 for the receiver.

Thanks for the info. My he barrel is not from the kit, I took it off a
Springfield 4800.

SAR 4800 are complete Imbel rifles imported by Springfield Armory, so the barrel is Imbel. Whether you sell the whole rifle or part it as kits you are still way ahead