Buy a dead center, or a live center, and use it as a gage.

Hmm... yikes! McMaster has 'em for $50 each...

Notice that's for carbide tipped, and $39 for high speed steel.
You should shop around a bit, how does $2.45 sound?
http://www.use-enco.com/CGI/INSRIT?PMAKA=251-
3062&PMPXNO=2606550&PARTPG=INLMK32
Of course, you don't get McMaster-Carr's famous next-day delivery
that way, either. :^)

I'd suggest you stick with a #2 taper, no larger for that diameter
stock.

Of course, another way to skin this cat is to use something
with the taper already bored in it:
http://www.use-enco.com/CGI/INSRIT?PMAKA=214-
8622&PMPXNO=2613662&PARTPG=INLMK32
http://www.use-enco.com/CGI/INSRIT?PMAKA=214-
8704&PMPXNO=945654&PARTPG=INLMK32
I think even Dave suggests this for the tailstock ram.

And last but not least, consider reaming your rough-bored spindle:
http://www.use-enco.com/CGI/INSRIT?PMAKA=891-
4730&PMPXNO=3904656&PARTPG=INLMK3

Later,
--Glenn Lyford