The neoprene (people call it neoprene but it wasn't really that) rear main seal can be used in the 1956 235. I'd suggest measuring the diameter of the sealing part of your crankshaft. I would have no interest in the rope seal. Ideally a one-piece seal would be ideal but you would have to get your block machined to accept it...by a gentleman named Jerry who also lives in Tennessee. If it was straightened up and polished when your crank was reground you may need to install a "Speedi-Sleeve" to restore the sealing part. Pressure has nothing to do with the rear main seal. You should ideally have .001" clearance between your main bearings and your crankshaft. That will keep your crankshaft from moving up and down and also will limit the amount of oil that will run past the bearing and down to where the crankshaft end piece is. Centrif. force is what will sling it up the back side of your engine block.
As for the cam...hydraulic or solid lifters? There are some solid lifter cam choices for you and if you're using hydraulic lifters the best option in my opinion will be something like the stock GM cam for the 1959 235. Lower lift and lower duration force it to produce maximum torque at a lower rpm and keep that torque in a long level line.
Others will be along to offer some thoughts soon...
