Milling Machine Taper question

I've got a slightly off topic question for you folks, if ya don't mind.

I've recently purchased a nice, old Milwaukee manual mill - it's got an NMTB
40 taper with .625-11 (5/8-11) drawbar thread. What other tapers can be
used in this machine? Can a CAT 40 be used? It seems to have the appropriate
taper and drawbar(actually pullstud) thread, although it's missing the
"straight" area at the top of the taper. BT 40 seems to have the right
taper, but a metric drawbar/pullstud thread.

Mine is shaped something like this:

| | <------ this is the "straight" part that isn't on
a CAT40 taper, as far as I can tell...
| |
/ \
/ \
/ \
/ \
| |
---------------


Can anyone help me out here? I need a decent collet holding chuck for this
thing to make endmill changes easier and they seem to be far more readily
available on the surplus market in CAT form rather than NMTB.

Thanks!

Matt King
Columbus, GA

P.S. Right now the machine has a B&S 40 to 30MM Taper Cam Lock quick change
unit in it. Great if I could find much in the way of 30MM Taper stuff with
the B&S CamLock notch already cut out!