WOW, what a neat build. That is a lot of work that you went through, but the end result is very nice! That process would make a nice article for a magazine or website.
My father fired the M3 105 in Europe in 1945 and ended up WW2 as an instructor on this howitzer. After the war he did some civillian jobs then went into the National Guard as a "redleg".
By the way, there is a nice video on US infantry weapons that concludes with some scenes of the M3 firing. It's at; http://www.liveleak.com/view?i=655_1240833450
Keep up the good work. We'll look forward to seeing more of your projects in the future.
Gary