I got some more work done on my engine yesterday and today. I've been working on the design as well as some house projects, so haven't spent much time in the shop lately. Hopefully I can start getting really serious about this engine.
Here is the engine base. It's a piece of aluminum about 8" long, 2.25" wide, and used to be about 3/8" thick. However, it had a bit of a bow in it, so I flattened both sides with a flycutter in my end mill. It's now about .335" thick, but it is nice and flat. I will probably cut down the length some.

Here are the cylinder assembly support blocks. I gang drilled the holes to make sure they were in as perfect alignment as I could get them. They are 2" wide, 1.375" tall, and 3/4" thick.

Here is a partial assembly of what I have so far. The cylinder support rods are 3/8" diameter. Probably could have gotten by with smaller rods, but didn't want to push it. I'm quite happy with the alignment and the fit of the cylinder support rods... nice, close sliding fit. We'll see if that's still the situation after I screw the end blocks to the base plate... :-\

Next, I will fasten the cylinder support blocks to the base plate. Once I get all the air passages and mounting holes drilled in the end blocks, I may mill them down some so they don't look so "blocky".
Chuck