Your GMC should have a 248 GMC engine and it came with a filter. Sadly, too many of them have been replaced by 235s over the years.
Your engine will of course run without it but it will probably run longer with one.
You need to determine if your 235 is a full oiler or not to determine how to rig a filter. There is a tech tip on this site that tells how to convert to full pressure oiling. Also use the "search" feature in the forums to learn how to install one.
