Yes, the rod bearings can be changed with the engine in the truck. Since you've probably got the early model 235, a main bearing change will be difficult. Check the stamped number on the machined pad behind the distributor to see if the engine is actually the same year as the truck- - - -a lot of things can happen in 70-something years, including swapping in a later model engine.
Small score marks and other blemishes can be polished out using a strip of fine grit emery cloth and a "shoeshine" motion on the journal- - - -just do a VERY good cleanup to get rid of the gritty residue. Measure the crankshaft for out of round and taper wear first- - - -a little is OK, but serious wear will require a full overhaul- - - -pull the engine and strip things down to bare bones. Have the EMT's standing by to give your checkbook a little CPR in that case! Back in "days of old when knights were bold", an "in the frame ring and valve job" and rod bearing change was a routine "minor overhaul".
Jerry
