Hi Pete,
This is going to be an interesting project and it's just a beautifully designed and proportioned engine. Nothing to be afraid of . . one part at a time . . umm, well in this case four parts at a time.
Dave, I don't know if this will be of help but I've just recalled I do have some information tucked which may (or may not) be useful. Some time ago I began collecting known, or newly discovered, errors in the ME Beam engine (the standard version) from builders I contacted. Here is a compendium, which is from various sources and in no particular order.
1. The hole spacing for the steam chest bearing mounting holes and the holes in the base plate do not agree
2. The hole spacing for the Governor bracket mounting holes and the holes in the base plate to not agree
3. The entablature distance from the feet to the mounting hole is 3/32 short.
4. The entablature slots for mounting the radius rods are not in the correct location. I established the location at assembly.
5. The crankshaft throw needs to be extended out 1/16" to allow the connecting rod to center on the beam.
6. The crankshaft keyway needs to be longer to allow for the key for the governor bevel gear. I extended mine to 3.362" from the end of the keyway to the end of the shaft.
7. The entablature stay is 3/32" short on the 2-7/32" dimension
8. The base of the main bearings should be two inches to match the base plate and pedestal bracket.
9. The valve crosshead - I milled 0.100" off the bottom around the center hole to give more clearance for the steam box gland and the lock nut. The locknut cleared the top of the gland, with the gland all the way down buy about 1/64". And it had to be turned just the right way or it hit the gland bolts
10. Problem with interference the parallel motion links and assembly. I had made the links out of solid instead of the multi part assemblies that the print shows. So the information here is how I modified the parts to work.
a. At the cylinder end of the beam there is not enough room for the links and pins to pass each other when the beam goes through its motion.
b. I removed 1/32 from each side of the end link pad on the cylinder end of the beam
c. I shortened the end link shaft by 1/8" so the distance between the two bearing fits is now ½" and shortened the bearing fits to 5/32 long.
d. I removed 1/16" from the thickness of the of the 2 cylinder end parallel motion links.
e. I removed 1/16" from the outside of the 2 parallel rods for a distance of about ½" on the end with the ¼ " bore.
f. I shortened both ¼ dia fits on the cylinder crosshead by 1/16" then I reduced the 3/16 dia fits to 5/32" long to match the parallel motion links
g. Since I made the links out of solid I made hex head screws to hold the links onto the shafts instead of the design shown on the prints.
11. In the views of the assembled engine a spacer pipe with a flange on both ends is shown between the steam pipe and the steam cock and throttle valve. There is no drawing for this and no length given.
Since all these items are from others, whose abilities and accuracy I can't verify, and I haven't begun comparing the information to the drawrings, I offer them only as guidelines or heads-ups. Your mileage may vary.
The original construction series in ME for the "New" ME Beam Engine" (which this is) by EXACTUS started 01 October 1959 (No.3038 ) and continued through 17 December (No.3049.) There was a follow-up article in ME on modifications to the cylinder 06 October 1960, and a further article on a fine example built by E.E.Hughes, 05 May 1972. There has also been a complete "new" construction series in ME since then (1990s?), the publication dates of which I don't know. There are of course subsequent to these articles a number of letters to Postbag sprinkled about.