It's new project time!

There's no point in doing small simple stuff, so to get my CNC juices flowing, it's time to build a sump-mk2-holding jig for the machine.
There's a few ground rules:
- The machine envelope is not big enough to cut a BMW sump in one go, so it must be possible to reverse the sump on the plate. That does have one benefit, I can do all of my clamping outside of the machining area, so there's a reduced risk of smashing cutters on clamps.
- The jig must be removable, and replacable, with minimum effort
- The jig must be suitable for a MadModder Projectitus
[shouldn't that be Projectitis? -ed] build log

- No actual jiggy-jiggy will be performed.
So... the first job is to scour the workshop for some suitable items:

I found the metal plate about 3 miles away at Mersey Metals

34 quid!! For a piece of 1/4" steel a mere 1ft by 1metre! Maybe it was the mixed measurements that put the price up... The big wax lump may look hauntingly familiar. You can probably guess where this is going...
The bit you didn't spot is the elderly worn out boring bar....

On the prowl for some blocks which would be a nice tight fit in the table slots, this old boring bar came up trumps. As it's truly worn to a nubbin, I am going to re-purpose it guilt free (even though it is high-quality tool steel....
So... here's the plan (apologies it's a little large, if I shrink it the text is unreadable):

First operations (on a slightly oversized piece of aluminium) will be to drill all of the mounting holes that can be reached. Some short dowels will then be screwed into holes on the jig plate, the sump is then turned around and put back on the plate, the dowels should drop nicely into the new holes providing an accurate position of the piece on the jig; the remaining holes are then drilled.
After that.... I haven't decided yet...
The clamp will probably be in the form of a strap going across the top, held down with 2 flange nuts, onto 2 posts which will be attached to the tabs on the plate. It will mainly be there to ensure the dowels aren't taking any significant lateral machining forces; but since I anticpate putting at least 4 & probably 6 or even 8 dowels in, I'm hoping it'll all hang together nicely.
Any thoughts? Am I on the right track or have I missed something dead obvious?