i have to comment on the conversion do detacheable models. Back about 12 years ago, there were 3 Chinese models that where widely availlable, 2 detacheable mag and 1 fixed mag. The main difference between the two detach models was that one came in the standard chinese military stock and one came in a beefed up, rubber buttpad, chu wood stock.
The first was to my knowledge a military D model and it's complete trigger assembly and the receivers dimensions at the trigger group attachment points are different from the second D model rifle. The trigger group and mag release lever (AK type) are unique to this military model and i don't think they were "modified" from a fixed mag version, or re-worked, they were made that way.
The second D model was refered to as the "north american Sporter" , thus the bigger more hunter sized stock. This model came with the little 5 round mags and has the exact same receiver and trigger group dimensions as the fixed mag rifle. This rifle, while it will accept a magazine larger than the 5 rounder, the mag release this model comes with will fail to securely hold a 30 round magazine while firing, the mag will drop out. This rifle was also different is barrel length, though i can't remember the exact numbers. These detach models are in fact factory reworked military fixed magazine conversions, but because of the magazine catch, are not meant to fire with military sized magazines.
A very handy gun smith type, could with the right tools, very easily convert a fixed mag sks to accept the 5 rnd sks magazine. NOT something i recommend you try yourself, unless.... you are a very handy gunsmith type hehehe

my 2 cents