As a point of interest, there is a Type 4 folding stock, and that’s the wire folder developed by the East Germans and used by the Romanians and Poles on either AKMs or their versions of the AK-74.
On East German MPi-KMS72 (AKM)
On Romanian AIR (AKM)
Polish Kbk wz 88 (Tantal) version of the AK-74
On all of these examples, except the Tantal, the standard Type 4A receiver was used. The folding stock was designed to secure using the rear trunnion normally used for the fixed stock, thereby making production easier and having more flexibility. The Tantal however, had an extra safety selector on the left side and therefore used an iteration of the Type 4A receiver. The last unique version of the Type 4A receiver is the one used on the Hungarian AMD-65. This also featured a folding stock that stowed to the right, but the rear trunnion, swivel, locking system, and strut itself were unique to the AMD. As such, the AMD has cutouts in the rear of the receiver to accommodate the folding stock and cannot be changed to a fixed stock version.