Well, I took off sick today and was thinking about what might be a good way to do the mod. There have been some members who have asked about such for some time -and
ALOT of yadda-yadda on the topic (probalby too much yadda-yadda).
Anyway, I had avoided doing the actual mod as I considered the options (there are quite a few different possibilities with pro's & con's to each). I had not really much cared about it personally -but it has become "a mission from God" (grew on me).
So, after getting my mind visually around the concept, I proceded to work it out with a Tapco mag & gun today, based on what I would use.
I got my thinking "outside the box" -everyone tends to think about using the cut-off duckbill, or making a new seperate duckbill, or something like the DC Engineering adapter...cost seemingly a factor...
Here is mine (my "adapter"):

A HK 6mm stock "push pin" that is approximately 1 3/4" long. It is smooth with a head and a spring set in the end to hold it in place via tension. I guess similar items could be used -I liked this (and it was in the junk box).
Taking a 20 round Tapco "duckbill" mag...

I removed the duckbill about 1/2" (this is not critical) away from the mag body. Then looking at the side of the remaining piece of duck bill, you see 4 "slots" -we'll-call them "grooves", and, 5 high spaces -we'll call them "lands".
Well, the
TOP 3 "lands" and
2 "grooves" are left in place -the
BOTTOM is dressed down to the mag body. What this now is, in this mod, is the front locking surface. FWIW, I picked this particular location to latch the front of thre mag after examination of the relationship between the rear & front of a AK mag. (BTW, that *is* some tuff mag material -a Dremel rotary cutter and sanding drum finish fit it nicely.)
I finally drilled a hole (yes, a hole!) in my T-6 stock that I chose for the mod. Roughly, this is located 11 3/4" from the
END of the stock (where it joints the "tube" ("stem") for the telescoping stock. The hole was approximately located then 1 3/4" from the
TOP of the T-6 stock.
The HK PUSH PIN pushes thru the side of the stock (I did so from the right -my habit) and it's spring holds it in place (nicely -can be removed with a bullet point). Then, the mag has the front locking portion go under the pin and latch at the rear as normal.
Correctly done and fitted, the modified Tapco mag goes in and out (with the drop-free bolt mod) just as a AK mag would -even easier. And, has the added feature of the SKS BHO! The set-up is
STRONG -really strong. It makes a nice slick modern rifle -I'm glad I did it.
Done so, as I chose, the weapon can be field stripped and returned to duckbill use, or, fixed mag use
EASILY via removal of the puch pin.
The
MAJOR ISSUE is placement of the hole and fitting of the mag to match it. This requires some skill -the project would be no more than a 4 on a 10 scale of difficulty if it were not for this...that makes it a "8-9". None-the-less, with reasonable care it can be "fished" (located) -the trick is to do this well and always make it
TOO TIGHT with
TOO MUCH MATERIAL...then, it can be fitted with care (material is HARD to put back).
Anyhow, there it is folks...did it on the cheap, and, without need for engineers and project designers.

I'll get around to some pics over the weekend.
LG

P.S -If what I said is understandable -you can do this (many members here can easily). If it is greek -
DON'T DO IT! I don't want to be held responsibe for somebody making a mess of things. And,
NO, I'm not going into production or doing it for anybody, 'cause I don't wanna.