3/4" Dia. acme threads sound great; super strong and they work smoothly. We can't wait to see these parts put together and functioning. That's an interesting historical photo you picked to show the elevation screw. The elevation screw, handle, collar and bottom yoke shown in your 1863 photo of Battery Rosecrans in the "parallels" on Morris Island, picturing Federal Siege operations in Charleston's outer harbor are all per spec. on the copy of the 1862 drawing we have of this carriage. At some time, a while before this photo was taken by Haas & Peale, this was a three gun battery with all three 100 Pdr. Parrott Rifles trained on Fort Sumter. One big rifle, to the right of these two shown, blew up, shattered clear up to and beyond the trunnions, probably due to the explosion of a faulty shell. This is a rare photo in that it shows Gen. Quincy Gilmore's seacoast gun crews in a "working" battery with all the mess that war always produces.
Lookin' good!
Mike and Tracy