restoring a Penn mortise lock

Hello,
I have several old mortise locks made by Penn Hardware probably around 1925 or so. They are all for interior doors and so either have rudimentary skeleton key holes or thumb bolts. I have removed them from the various doors in my apartment.
I want to open them up, take off all the layers of paint which have accumulated on their external surfaces by soaking and scraping, lubricate them, and reassemble them. I've been able to do this successfully with three of them -- the ones with thumbscrews.
The ones with key holes are nearly identical, except that for some reason, the "exterior plate" (I don't know what to call this, the piece that is visible when the lock is installed and which has been painted over a hundred times) is not screwed onto the casing, as is the case with the others. Rather, in the place of screws are what looks like some kind of bolts or nails -- there is no slot in the head. And on the inside, the other end of these bolts have a weird sort of "plus" engraved in them which extends across both the bolt and the casing, like it was burned in while it was hot or something. Sorry if this description is poor, I just don't know how else to say it.
So my question is, is there any way to remove something like that? And if not, what is the best way to go about getting the paint off these other cases?
Thanks for any help -- I appreciate it.
Ivan.
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Joe's right, they're rivits. Drill them out with as small a drill bit as will do the job. Try not to enlarge the original holes.
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Ivan Drucker wrote:

No plastic in those things, soak in MEK, acetone, or lacquer thinner for a few days and rinse them off. (standard safety disclaimer, no open flames, electrical arcs, smoking, low yield nuclear devices, etc. around fumes) Dave
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