There is a couple of books about the 348th you might be interested in, the first appearears to be a unit history written by Keith Bryan intitled: "Pack up and move; a pictorial history of the 348th Engineer Combat Battalion".
it is currently not availible on Amazon & a WorldCat search only shows a copy at the New York Public Library. You might want to try the Library of Congress.
The other is: "From Boston to Berlin" by Roland Regan Jr.
http://www.bostontoberlin.org/index.htm
As far as finding out what company he was with, the best thing to do is is to obtain his personnel file ( ask for complete 201 file)from NARA in ST Louis. you can use EVetrecs at the NARA website or send in a form SF-180 request.
Unit records for the 348th will be found at the National Archives in College Park, Maryland.