Whoa, whoa, back-up.
rbs56, 55.5 means 55 1/2 or 1955 1st or 1955 first half year or series.
I looked at your profile and you say you have 1955 GMC 100 2nd series.
Big difference in track width. You may be able to do a later year truck IFS parts swap as "J Lucas" mentioned.
Please identify which half year you are asking about.

"Adding CFM to a truck will only help at engine speeds you don't want to use."
"I found there was nothing to gain beyond 400 CFM."