I think you could take this in the direction of Pgrens and make the upgrade a little better but cost more. It's a little risky b/c of how infantry changes can go wild, but G43 grens seem like a rather marginal ability currently due to how many other infantry units such as tommies, rifles, and even cons have more expensive and ultimately better upgrade paths available. It's not a bad ability but it's nothing special right now. Pgrens on the other hand...
I think you neatly summarized my point here about g43s in their current state being a lackluster upgrade with very marginal role despite being included in 3 (three) commanders meaning someone at somepoint thought g43s are really useful
Upping the muni cost to 60 and adjusting the performance accordingly would seem like the easiest solution. The less riskier way would be to keep g43s performance at the current state and match the SVT cons/ ppsh penals timing by reducing the CP cost.