It probably is a 361, looks like a LB 383. If it has the 440 "step" accross from the dist. it is a RB 383. Although that motor was a higher end for Dodge and Desoto. The 350 was a 1958 motor, but it could of lasted into the early model year of 59. Chry. was trying to find its way once the HEMIs were dropped and all the changes that all the motor companies were fighting over with a downturn in the economy in 58 (recession).

My vote, site unseen, is that it's a 361