I purchased the Marlin used this past October and it was outfitted with a Llebroc Marlin helm chair and the Bench seat was on the passenger side. We preferred the helm chair to match so we ordered a matching chair and pedestal. The pedestal at the helm station was an adjustable type and it's lowest setting was around 7" I wanted a fixed model and Llebroc offered them starting at 6'" in height and the next size up was 12". We bought the 12" and took it to a machine shop to have 3" cut off. The previous owner must of had the bench seat installed because upon removal we discovered the hole pattern for a pedestal base. And the pattern differed from the Springfield pedestal we purchased. There where no identifying marks on the helm pedestal but my best guess would be it's a Garelick. Both Garelick and Springfield make a 9" base (Llebroc sells Springfield) but the hole pattern is slightly different. I'm going to replace the pedestal at the helm station too with a fixed model to match the one I just installed.... In each case I just rotate the base to drill a different hole pattern between the existing pattern. You can drill the detent stops for the chair lock if you prefer after you set the chair in place and establish some witness marks.
I'll be grabbing some pictures of the bench seat this coming weekend as I have no more use for the seat so it's for sale if anyone is interested.