Looking for some help on this one...

I found an inexpensive, old Mossberg 20 gauge and want to try my hand at the gamut of shotgun “smithing.” There’s a little rust, the bluing is so-so, the wood is beat up, etc. And, I’d like to cut down to 14”.

I do understand the NFA process and also that there are some advantages to 590’s, purchasing a kit from Mossberg, etc, just not the direction I want to take.

Any good build links, tutorials, good pictures, and so on?