Am I crazy to design my own stationary engine?

I have never built a piston based stationary steam engine before but have been considering it.

I am in the process of building a model of a quartz crushing stamper used during the gold rush in New Zealand in 1861-1872. My wife was crazy enough to suggest that it wouldn't be complete without a steam engine. I think she likes to get me out of the house! But I trape back in covered in swarf! Besides she runs a web site about the Gold Rush and wrote a book about it (KaeLewis.com).

I have a block of solid brass 50mm x 38mm x 150 mm and some bits and pieces of brass and bronze round stock. After watching a YouTuber make a functioning engine by putting a piece of copper pipe as a piston inside another copper pipe I thought I could do that too! Better still, rather than make all the components separately why not use this block of brass I found at a scrap metal dealers.

I could make a two cylinder engine or a two stage compound engine by boring two cylinders in the block with two piston type valves bored alongside them and galleys drilled straight through from the side.

I don't have any honing equipment. I have a Boxford A lathe and a drill press and hand tools. That is IT. Brass can be polished up very nicely with 1200 grit and Brasso but that might distort the dimensions a bit.

I have been reading about silicone or Vikon piston rings for steam engines. I don't know whether I can get them in New Zealand. Could I get away with no rings and sloppy engineering? I doubt it.

I know how the plate type valves work, but not much about the piston type, and don't know how to go about timing, except that watching Mr Appleby I learned that steam should enter before TDC to cushion the movement of the piston as it reaches the top.

I would like to consider a D-link valve system if it is not too complicated. I love the idea behind their design but don't know quite how to go about setting up linkages to slide along the D-link. I took photos of a steam boat in Connecticut which had D-links but cannot make out exactly how the operator moved the mechanism along the D. Or should I just keep things simple?