Changing dimensions of downloaded base

[adampaskowitz]

Our base is about 3" wider than the long base, so I've been trying to modify the downloaded bases in Inventor. It seems like if I could lengthen Sheet Metal Front-Back_19 and Churro cross link and Screws_20 by 3" each, everything would be fine. I've tried to Direct Edit them, but that creates a mess. When I resize the parts, the extra material just hangs off the sides. I've looked at the help screens which make it seem like I ought to be able to cut a part in the middle along a plane and then extend it, but the downloaded parts have no faces or individual features I can work with. Is there some way to adjust the dimensions of the base?