Do you think the Forster Universal Drill and Tap Jig is accurate/rigid/sturdy enough to redrill slightly off center/canted/buggered 6x48 holes to 8x40? Or will the drill bit just tend to follow the old hole and reproduce the same error.

the difference is too small for a drill bit (of ANY short length) not to drift

tig and redrill

jeffe

Or mill it.

The proper tool is a short endmill, with the action in a vise on a mill. I wouldn't trust a drill jig for that operation, and definately would not use a drill bit.

Here's a question(s) regarding milling the new holes.

What type of end mill is prefered or does it make a difference. I mean centercutting vs non-centercutting, two flute vs four flute. Also, since the tap drill is a #28 (.1405") for the 8x40 screw I presume that using a 9/64 endmill (.1406") would suffice?

Thx.

Since you already have an existing hole, you don't need centercutting. As I recall 4 flutes are generally stiffer than two flute, because the flutes aren't cut as deeply. 9/64" sounds good.