Sell it as is. The cost to build a full rifle would put you in underwater.
Rifles are worth more as parts than as a whole unless it’s something REALLY rare.

Value is hard to say. You’d get the most out of breaking it up further.
The barrel sounds really nice so maybe $250.
Trigger assembly is a dime a dozen. Perhaps $20.
Receiver is harder to value. I’d say something like $100 or $150.