I am having a little trouble centering my router on a table insert.

I picked up a Skil 1825, and a Freud Universal Router Table Base (the
black phenolic one with the red and grey inserts). The problem is that
in order to mount the router, I have to use the router baseplate as a
drill template, and centering it on the table base after removing it
from the router is pretty much a hit and miss operation.

What I did so far was:
1. unscrewed the router base
2. put a Freud guide bushing (3/8" ID) into the table base insert
3. mounted a 1/4" pilot bit in the router collet
4. put the router and base on the table insert, with the pilot bit
centred in the guide bushing as best I could
5. Taped the router base edges to the table base
6. Clamped the router base to the table base
6. drilled and countersunk holes (with drill press) using the router
base mounting holes as guides.

I think I may have let something slip a bit, and perhaps did so even
after I drilled the first two or three holes. I can just get the
router attached to the table base. It's difficult because one or two
of the holes are visibly offset after I line up two of them.

The end result is that when I put in the 3/8" ID guide bushing and the
1/4" pilot bit, the bit is in contact with one side of the ID of the
guide bushing. So, it's close, but I want it closer.

I am considering messing with one or two of the holes I drilled,
perhaps enlarging the appropriate holes to try to swing the centre
into alignment, or perhaps drilling another set of holes after
rotating the router a bit.

I am also considering through-drilling the threaded mounting holes and
tapping them for 10-32 (8-32 in there now). This way, I could centre
everything up. then drop a bit down through the drilled out holes and
starting a hole in the table base by finger twisting the bit..

I might even be better off turning a hunk of aluminum with a 1/4" or
1/2" 'shaft' and a shoulder the right size to fit the opening in the
Skil base.

Anyway, I have seen some great answers here, and wonder if anyone
might have a suggestion as to the best way to proceed.

Thanks,
Larry