compur
Been spending a lot of time on here!
I see three MR-9 adapters on eBay USA right now ranging in price from $9-$14 shipped. Since you only have to buy it once and can use it on any number of cameras, it seems like a pretty reasonably priced solution to me and does not require any of the above tinkering.
I'm thinking there's a bit of chance that the HK knock-offs don't really deliver.
I have several that I've used for years and they've worked fine. The MR-9 is simply a metal case with a diode in it. The diode in the originals probably comes from the same place as those made in HK.
Battery woes aside, 60s-70s SLRs aren't exactly free of age-related issues. With camera repair usually exceeding their cost(assuming you can find it), old manual bodies can be a crap shoot now. Not sure anyone just starting film photography wants the headaches.
Yes, it's terribly adventurous and should never be attempted by wimps, whiners or weenies.