I think that this was lacking:
First of the series is a BTR-50P without roof but with a pintle Degtyarev 12.7x108 HMG. The most numerous of this APCs was BTR-50PK with roof and with a pintle Goryunov 7.62 x 54R MG. This model is very similar to the Czech OT-62 Topas, which had a small turret for a 7.62x54 MG. The last and most different vehicle is a polish Topas 2AP, with a turret armed with a 14.5 HMG and a coaxial 7.62 MG, and amphibius gear.
Credits: My drawing is based in Glorfindel's PT-76 ligth tank. Cheers.