3100 frame channels are 5-3/4" deep while 3600 frame channels are 5-27/32" deep, so about 3/32" deeper. That's outside-to-outside dimensions.
Channel thicknesses are 9/64" for 3100, and 3/16" for 3600. So if the 3100 plates are a full 5-3/4" wide, you might get by with them.
Info is from the '51 Chevy Truck info from the GM Heritage center. Should be the same or close for '54.
GM Vehicle Information Kits
