That is a good point about someone possibly having tapped the holes for a modern thread. Here is a URL giving a guide to the current American threads, which I believe should be fairly readily available in brass. Old American-made electric fittings are also worth exploring for useful screws.
http://www.sizes.com/tools/thread_NCNF.htm
Judging by later Pfluegers, the heads of modern screws are likely to be too bulky. I'd spin them in a drill and reduce the head on stiff or stuffly-backed abrasive paper. Ther much higher-speed Dremel tool is even better, but it comes with a restricted variety of collet sizes, rather than an infinitely adjustable chuck. Tou could tap a piece of brass tubing (K&N. from a model-making shop or eBay) to hold the screws.
Dremel's tiny cutting discs may be a good way of deepening a slot, or a junior hacksal blade with the wavy sides ground flat. The best, though, if you have a belt sander, is a bflad needle file thinned and ground smooth except for the edges.