Pro Concept was a short-lived late midschool brand, that lasted from about the late '90s through to 2003.
The frames were being made by a couple of different frame makers over the years.
I believe that the same frame makers were also involved in Dingo, Cheeta, and American Bicycles, as you can see a "family resemblence" in these frames.
The initial PC frames were aluminum, and were available in sizes Pro, XL, XXL, and XXXL.
TT lengths were 20.5", 21,25", 21.75" & 22.25" respectively.
The 24" frames have a 21.5" TT.
I have heard of an elusive 22" TT cruiser version out there, but I am yet to see one.