Hi Alec - How's that going? If I was doing that, I'd try to brace those clamp plates downwards into the column somehow with more (at least 1/2" steel) plate. Would not really like to drill the original casting, though. I've thought of raising my Benchmaster vertical head in that manner just to have more headroom, but so far the twin clamping plate idea is the only one I've seen to do it, and I'm not too convinced of the rigidity.
I do happen to have a nice piece of 2-1/2" precision ground heavy-wall tubing. Might end up mounting my 1/2" VS wood router on the end of it(!) Should be fun.
Well, let's know how it goes.
cheers
Shaggy