I just bought a steam engine! It's pretty exciting - steam engines were the basis for the industrial revolution - long spinning shafts running through a factory with pulleys from which belts would turn drills, saws, presses, looms - whatever. I don't have a boiler - yet! This seems to be an "oscillating" type which has a camshaft-run valve which allows the steam to push the piston on both the upstroke and the down stroke. I don't have tools of the size needed for this, so I ordered a new set of wrenches.

The 1.35V batteries are mercury oxide cells which have been outlawed in this country and MOST of the world for quite some time. I use common #675 zinc-air hearing aid batteries in my Luna Pro and a number of my Konica cameras. The #675 battery is smaller in diameter than the original PX-625 mercury oxide cells but they still work fine as-is.

If the loose fit in the battery chamber bothers you, find a small O-ring at the hardware store to fit around the zinc-air cells to take up the extra space. The zinc-air cells are also a little thinner than the mercury oxide cells so sometimes I have to ball up a tiny wad of aluminum foil and place it on top of the cells to take up the extra depth.

The Wein cell is also a zinc-air battery EXACTLY the same as a #675 hearing aid battery except the Weins are much more expensive and have only one air hole in the bottom vs four in the hearing aid batteries. Supposedly having only one air hole gives them a longer service life but I have used both and can't see much if any difference myself.

Zinc-air batteries do have a short service life of 6-12 months or so, but they are pretty cheap and they come with the air holes sealed to prevent premature discharge, so an 8 pack for $8 or so could last you 4 years or better.

I also have this adapter for my Nikon F Photomic which very nicely solves the loose fit problem:
http://www.ebay.com/itm/NIKON-F-PHOTOMIC-FTN-TN-METER-PRISM-BATTERY-ADAPTER-/152002598077?hash=item23640f94bd:g:BAoAAOSwLVZVg1vu
If you do use this adapter, follow the instructions exactly. The polarity of mercury oxide cells is opposite that of current batteries so it is quite easy to get either the batteries or the adapter in upside down and it will not work that way. I rushed the installation the first time and it didn't work; I went back and followed the instructions step-by-step, and it worked perfectly - and its damn convenient to boot!

You can also use silver oxide LR44, AG12, 357 or 303 batteries - these are what I use with my Nikon adapter. Silver oxide batteries are 1.5V vs 1.35V for the mercury oxide cells. The increased voltage will make the meter think it is seeing more light then there actually is, so the meter will give you readings that will result in underexposure of 2/3rds to 1 f stop. To compensate set your ISO (ASA on the Luna Pro) to one stop faster - for example, if you are using ISO 100 film, set the Luna Pro to ASA 200 and you will get the correct exposure readings from the meter.

Note that you must use SILVER OXIDE batteries, not alkaline batteries. Alkaline batteries drop in voltage significantly over their service life and will give you inconsistent meter readings over time. Sliver oxide batteries have a near-constant voltage for their entire service life and will give you correct meter readings all the time.