From "Bf 109 G/K, Field Conversion Kits (Rustsatze)", Harald Voght, 1998, Schiffer Publishing. Pag.55: Bf109K-4, Rustsatze IV: 2 wing gondolas each having an MG 151/20.
From: Bf109K-4, T. Poruba, A. Janda, 1997(?), JaPo Publishing. Pag.80: Rustsatze R4, two additional MG 151/20 (135rpg). Pag.23 (in Czech) Bf 109K-4/R6, diagram with wigpods mounted. Pag.36 (in Czech) Bf109K-4 armament, altenatively: 1xMG151-20 engine mounted.
Any other source to understand better the matter? Thanks for help.