Rick, you'll probably need a 620 take-up
spool but it can't hurt to try to load a 120
roll into the film chamber. I shoot Brownies
and I've found that some (e.g., the Brownie
Hawkeye) will readily accept 120 rolls while
others (e.g., the 1930s Six-20 from the UK)
can be made to accept 120 rolls with some
minor modifications.
Have fun with the Duaflex. There is a guy
over on ModelMayhem, Click Hamilton,
who shoots only a Duaflex -- see his work
(NSFW) at
www.clickhamilton.com .