I found this old post on Jockey Journal of my frame... before I bought it, that explains why it has a straight center post.
"I think I got this bike stuff figured out , for over 20 years this motor was in a 53 wishbone frame with a 8" over shaved wideglide no front brake and star hub , jock top suicide shift and upswept megaphones , pulled the motor and put my spare 55 motor in it.Had Painter Joe at Williams Brothers motors rebuild it . The frame is a original Motor shop frame built in Oxnard ,like the ad says I picked it up from a guy in San Jose that had changed the center post to fit a evo in it . The mids came from KD Engineering in Concord ca." - hdtt60 on Jockey Journal