We finally got around to pulling the small block out of the 3500 today, despite the Goodwrench 350 stickers on the valve covers she displays all the indications of being a junkyard engine swap at some point. Casting # checked out as a '87-'95 350.
I'm no expert, but I think you are supposed to have more than three bolts between the flywheel and torque converter. This had three, the rest of the holes don't really line up.
I'm not sure that this is the flywheel/flexplate for a TH400. (After I pulled the crank bolts)
As soon as I find another flexplate I'm going to do all the basic stuff, new oil pump/tube/pickup. New double roller timing set, all new gaskets.
I took the Accessory mounting bracket off to work on the engine, and underneath are all the old familiar mounting holes I'm used too. Strongly considering ditching the serpentine system for something a little more traditional.