G kit to Underfloder

What is the best way to build my G kit into and under-folder or side folder?

The side folder would be easiest, all you would need to buy is a folder stock like this.
http://www.floridagunworks.com/Merchant2/merchant.mv?Screen=PROD&Store_Code=FG&Product_Code=1508&Category_Code=AKA+AK+STOCKS
This is the stock you need to use, but I'm sure if you look around you can find it cheaper.
I have seen them selling for about $50, but it looks like everyone is sold out.
It is an easy swap, just take off the fixed stock & this will slide right in put in two screws and your done.

https://www.apexgunparts.com/./product_info.php/cPath/21_89/products_id/55?osCsid=3f10262195fd9b07c461ea81bc716a1f

What is the best way to build my G kit into an under-folder or side folder?

The Polish Tantal sidefolder stock and the Romanian sidefolder stock (shown above from APEX) mount directly to the standard AKM rear block found in the Romanian G (AKM pattern) parts kit.

Other original AK sidefolder and underfolder stock sets will not attach to the standard AKM rear block. There are at least three different underfolder rear blocks for the underfolder stocks - AKMS pattern (Polish, Hungarian, Russian, Bulgarian), Romanian (MD63 model), and Yugo (two different widths, based on receiver type). There are a couple commonly available side folder stocks, each with its own rear block - AKS74 (folds to the left) and AMD65 (folds to the right).

Because of the many different underfolder and sidefolder rear blocks, choice of receiver will depend upon what rear block is used in the assembly.

There are also a few U.S. made adapter pieces that attach to the standard AKM rear block and allow attachment of particular sidefolding stocks or collapsible stocks or some combination of both. Companies that offer such U.S. products include VLTOR, Ace RifleStocks, Advanced Technology, and TAPCO.

The easiest way would be to buy a Polish or Hungarian rear underfolder trunnion and build your kit on a Nodak model NDS-P1 receiver.

Installing the underfolder itself is a bitof a pain in the ass, but you'll get it.

Here's a link with step by step picture instructions.
http://home.earthlink.net/~mwsjb/AKbuild3.htm

Good luck