You're probably sick and tired of my guards suggestions, so here's one more to cheer you up:
since tank riders were used to defend against panzerfausts at close quaters, how about an upgrade for guards. I know they have grenades and an awesome long range weapon, but it'd fit their role as tank riders if they had a 50 mun or so upgrade to pps-43s: the reasoning being that the original squad is good for range, while the upgrade gives the guards quite a kick against at guns and infantry
another upgrade: for katyushas, the option for more racks. At a cost of 150 mun, the salvo is tripled to 48 rockets, giving a very powerful attack, but in addition, there is a significant increase in reload time