I have heard that there is a larger bolt-on brake assembly for the MB. Would appreciate any advice on where I could acquire a set and info on how much they will improve the ability to slow down and stop.
I think what you heard about are (or were) the kits that upgraded your brakes to 11" X 2" shoes & drums. Although it is HUMONGOUS improvement, it isn't as good as discs. The advantages of the disc brakes on your little jeep are that they hardly ever fade (compared to drums), work well even after a dunking (driving thru water), & don't wear out rapidly when you pack them full of mud. As Bob N. stated they can be expensive & complicated to adapt, irregardless of what the donor was (CJ, Eldo/Toro, Brazilian kit, etc.)
The 11" kits that were available several years ago were nothing more than (1974) CJ-5 (or certain wagoneers, Cherokees, CJ-6, etc.) brakes. They are an easy bolt-on project with no other mods (but a dual master cylinder would make things that much safer!) needed to fit them. (I do not know if they clear combat rims.) IMO for an MB/GPW the 11" brakes are a good, safe, affordable, easy to install/un-install modification that isn't so complicated that you make it unsafe due to a lack of understanding. The larger piston bores don't seem to deplete the master cylinder & repair parts are readily avalable. If you can't find or afford the kit you could possibly buy all four sets at a junkyard (backing plates, drums, etc.) & rebuild/replace the worn components. Before I upgraded to 4-wheel discs on my '62 CJ-5 I was happy with the 11" conversion that I bought from Four Wheel Parts Wholesalers in the late '70's (except when wet or when the mud would pack in there & wear out a set of shoes in one weekend!
) & I have 36" diameter tires on that & the vehicle is considerabley heavier than an MB/GPW (& heavier than it used to be).