MTW-II - is there a mod that does this ---

I can change the year count to 0.5 so that each turn is half a year but for history's sake, I'd then like to change build and training times to 4x longer and I understand this is not so easy but doable. I'm wondering if anyone here knows of a simple mod that has done this?

I'm not aware of a mod that does specifically what you ask for. However, editing build times shouldn't be that difficult (IIRC it's only a single entry in the export_descr_building file): it's just annoying to have to do it for every unit at every building level.