[Proj] Stupid Newbie Question - Projecting out of NAD27

[bsupnik]

Hi Y'all,

I'm working with data that appears to be UTM referenced against the 
NAD27 datum.  I'm using a line like this to init proj for conversion to 
lat/lon:

+units=m +proj=utm +zone=%d +ellps=WGS84

As might be clear, WGS84 isn't the right ellipse for this...I want my 
data to end up lat/lon for a WGS84 ellipsoid...what set of proj 
arguments will cause pj_inv to go from NAD27 to WGS84?

(Please forgive my misuse of terminology...I'm still getting used to 
this whole projection/datum thing...if it weren't for Proj's existence 
I'd really be screwed!)

*cheers*
Ben