Hey Brendan,
I missed this string before and am just catching up. I notice that you have been focused on his time in the engineering unit. He only started that in early summer, 1944. Until then, he was with artillery units as he was, actually, a trained artillery officer. Your Record of Separation (ROS) mentions Construction Engineer in block 27, but he wasn't trained as such - at least not by the Army or officially. He may have been a civil engineer in civilian life (as was my grandfather before the war) but he went through artillery school in 42-43 (58 years before I did). Even prior to that, he was serving in Field Artillery (FA) units. I would do the same research but with the 172nd FA (Regiment) and the 941st FA Battalion and see what you get there. He only did the engineer thing for the last 5 months of the war. The ROS just recorded his last known gig, if you will.
I noticed he would have been in his forties during the war. They must have thought of him as the grand old man of his artillery battalions! In my battalions (very different time and make up, of course) there were maybe only a handful of folks over 40. CO, SgtMaj (maybe) and some of the master sergeants/first sergeants (E8s) (maybe).
And what did he do in Honduras? (Block 12 on the pink form). Seems he spoke a smattering of Spanish (block 18), so that ties back into spending so time in Honduras. Was there a job there he did?