How about this frame fixture design?

So I'm taking the first step towards customizing my first bike, and that first step is building a frame building fixture. I've been taking machine shop classes, and have access to a mill and lathe. I have only basic welding skills and no easy access to a welder, so I'm trying to do this all w/out needing to touch a torch. If you can weld like a mad man, you'd probably come up with a different design.

I also know that there are a million ways to do this, especially depending on what kind of bikes you're expecting to throw on it. I'm expecting to be playing with mostly Vintage British (and some Japanese) bikes.

I've done a lot of homework. Some of the better links I've come across are:

The Chopper Handbook section on Frame Welding Jigs
The Bitter End Choppers YouTube Walk Through
This MechWerks page
The Knucklebuster .pdf on Frame Fabrication and the Frame Jig pages
Several threads on this site including this one

And i'm sure several others I'm forgetting.

With that said, these are rough sketches that I'd love to get people's opinions on. Once I settle on the design I'll be making exact blueprints for myself to work from, and will be more than happy to make them available to anyone who'd like them.

The design I came up with was based heavily on The Bitter End design, where they use two 3" x 2" rectangular tubes for the base and drill 1/2 holes to bolt up vertical adjusters. I don't know those guys, but I want to thank them for a super-helpful walk-thru video.

In this design, the vertical beam for the rear axle support would be fixed horizontally in position, but the rear axle plate is adjustable vertically. There is also a slot in the axle plate, which would allow 3.5" of horizontal fine adjustment.

In the front, for simplicity, I'de use the same design as for the rear axle, but with the usual steel bar / steel cones combo for holding the Steering Head in place.

The vertical beam for the Steering Head support would bolt into a set of four 1/2" holes drilled through both bottom beams. The holes are spaced at 2" increments to give a total of 13" of horizontal adjustability (plus the 3.5" in the vertical adjustment clamp.

Because I need the center frame beam to be very adjustable, I wasn't going to drill 2" spaced holes to pinch it in place (It will bolt around and underneath the main rails, to pull it down into them). Consequently, there's nothing in the center of the fixture to bolt the two rails together, to add stiffness and to keep them from wandering.

My plan was to drill two sets of holes on either side of the center of the fixture where I can bolt in a 2" wide piece of tubing (to the right or left, depending on where the center fixture is) to provide that extra support.

With that in mind, any thoughts on the design from people who've had the trial and error of trying to do this before? Suggestions? Criticisms? Some bit of adjustment I haven't included that might make life easier? It's a lot easier to change the design now before I start cutting metal.

If it's at all hard to visualize, look at the Bitter End chopper video, that'll give a much better idea.

Thanks!
Conn