The helmet will never accurately show an FJ helmet, it simply is of the wrong shape. No amount of shaving/transforming is really going to be able to stretch out the shape to match the curves and form of the FJ helmet, much less fact that that thing's liner is quite different, and has quite a bit different set up on riveting. My suggestion would be to simply get a repro FJ helm for like 70-100 bucks, unless you want to shell out 2-3000 for an original, which I doubt you do.
As for the other, I assume you just got a repro? That's just a standard Stahlhelm, used by all branches of service throughout the war in various models with minor cosmetic differences (like rolled brim, complexity of vent holes, etc). You can really do whatever you like, but if you want an actually correct paint job, I'd send it to Alexander and Sons for a full paintwork.
http://www.alexanderandsonsrestorations.com/
In terms of SS stuff, this is the kind of work he can do to make it actually look like a war-time SS helm:
http://www.alexanderandsonsrestorat...for-sale/m42-size-6658-ss-italian-front-camo/
In terms of FJ helmets, FJ helms are the one the few German helms he will work with repros on, due to the exorbitant cost of original FJ helmets (and the general poor quality of Stahlhelm repros, no one can ever seem to get the shape right, something is always exaggerated. The latest runs of repro WW1 Stahlhelms flooding the market have been termed 'duckbill-brim' helmets for a reason....). This is a good example of his work:
http://www.alexanderandsonsrestorations.com/project/m38-fj-three-color-camo-whalf-wire-basket/