Thanks Nick, I actually spent most of the time thinking and starting at diagrams of normal steam chests, and this kind of precipitated out as a side thought. My drawing may not be fully sufficiently clear, because I actually think this will be simpler to machine than a normal steam chest, but I could be wrong.
on the angled ports, they will be a hassle but doable I think. The milling machine i have access to has a colletted drill chuck, so it can easily be used as a super-accurate-versatile-manueverable-heavy-duty drill press, so that is where I will be doing them.
on the tolerances, I think I can do it. If I can't get a good enough seal with just the metal, I may try and mimic something like fork seals and piston rings. The shop has an excellent set of reamers though, so I think I got atleast OK odds that it will work out with just metal-on-metal.
unique/original is something I am kind of going for, so thanks for recognizing its potential there. I'm pretty sure I'm going to give it a shot, so hopefully it also works

I turned the cylinder earlier today, and it came out beautiful. It's about 1.15" outer diameter, 3/4" bore, and about 2.25" deep. I havn't done the piston yet, but the stroke will probably be about 1.5". I made it from some 1.25" round brass stock. The bore reamed well, and it's just buttery smooth. will post pics of it later.
-Jon