Harry_
Try looking at the small 1 hp Senco. I've been using one in a sys5, with 50' 1/4" hose, (3) guns (16, 18, 23ga) , and some glue bottles for 4-5 years now. Also put the sys 2 "attic" lid on top for brads/pins.
The compressor frame needs to be modified (cut off), but fits well. I run it all day with the lid closed, no issues.
I have a pic of my set up here somewhere, but can't seem to find it now. (My 20th century brain betrays me once again)
dan