The G-5 was closest to the G-6, especially in performance and firepower, it was only above 20-something K alt (mentioned above) that it improved this performance.
I say the weapons match a G6, the performance under most alts it will fly in AH is the same as a G6, it was closest to a G-6 in timeline.
Just do it as a G-6. It really is the best fit. G14 is the only other alternative, and that's just for the erla haube.
Ignore the bulged nose for the MG131s, and the rest is basically a G-6.