Brian,
The slotted screws are the famous stovebolts. Loose them at your peril! :>)
You really should read the engine section in the shop manual before you put the motor back together. The shims are critical as they set the oil clearance between the crank and bearing. Since you have the crank out, why not have the journals measured so that you can be sure of what you are working with?
Here are some links to the old Chevy car manual project:
1954 truck manual 1955 second series shop manual I took a look at the engine section of these two manuals and noticed that the 1955 second series engine did not use shims on the main bearings. So you might want to double check what engine you have too.
Good luck!
Kurt
