milling spindle on a CNC router

Hey all,

I've got a small cnc router that I would like to use to do some head
work on a Subaru motor. The problem is, it's set up for a porter cable
router, and it turns way to fast for what I'm going to do. Any one out
there make a milling spindle for their router table? I'm looking at
about 6000 rpm or so. I won't be taking real heavy cuts, just a lot of
3d milling.
machine details: 1" thomson shafting, linear ball bearings, ball
screws, 18"x24"x6" axis range. All alluminum construction. (I'm a
machinist)