How the heck do I tram the tilt in this fixed-head milling machine?

I have an old Millport CNC milling machine. This link is not mine, but it is *exactly* the same style of machine, and you can see how the head attaches and comes off: https://salvagedcircuitry.com/90s-cnc-revival.html

Near as I can tell it's held on by a mere four bolts!

When I first got it years ago, I trammed it with the help of the dealer and I absolutely cannot remember how we managed to do it. Unfortunately, years of temperature cycles thanks to living in an unheated shop have pushed it pretty far out of tram in both the nod and tilt direction. I think I understand how to tram the nod portion -- shims in both of the upper or both of the lower bolt sections as appropriate (in my case it's nodding backwards, so I'll need to shim the top). But I'm also tilted pretty badly counterclockwise when facing the head, and I'm puzzled on how to tram that out. Any ideas?