I had a friend with access to a 3D printer who was nice enough to print out some models so I could test fit the parts before sending them to the machine shop. And it's a good thing too because I found a few measurement errors and fitment issues.
Also, I could have easily made these parts myself as I have a lot of experience on basic machine shop tools, but work has been super busy with no time to spend in the machine shop and they kind of discourage that sort of thing anyway. As a result, I found a machinist who works out of his garage and charges a fraction of what the shops charge because his overhead is super low. Still, to save a bit more money, I opted to do the thread tapping myself to save an hour or two in labor. This is easily done at home.
The key to threading anything is to be steady and gentle. Do not force the tap. Doing so will probably break it off in the work piece. Lots of lubricant helps prolong the life of the tap and reduce friction. There are nice lubes for this purpose, but I just use ATF because it's sitting around. Also, make sure your work piece is firmly secured to prevent snapping the tap or tapping it crooked/ovalized. Aluminum is generally a good material to start with.