you can clean the rust out from inside the brake drum but it will just come back again. It will not effect the operation of the brakes as long as the area that the shoes comes in contact with is in good shape. If its heavily pitted or has grooves worn in it than you might want to get a new(er) drum or see if it can be turned down on a lathe and still be in spec. Doubt that a front drum on a 185 is going to have too much wear on it though. Just clean all the brake parts real good with brake cleaner, lube the pivot points and throw in some new shoes... good to go. Biggest thing is to make sure the o-ring or gaskets are good to prevent mud from getting inside as that is the biggest culpret to ruining drum brakes on these things.
My first Trike was a 185 as a kid... Loved it!!! Have fun, take your time and good luck!!!
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