Just got my donor engine today and started taking everything off and cleaned it up some.
To the left and right of the distributor under each spark plug execpt fot cyl #1 are white painted on letter. under cyl# 654 is the letter D cyl# 3 is a C and cyl# 2 is D. cyl# 1 the ac bracket is in the way but i didnt see a letter behind it.

so what do these letters mean??

 

IIRC, they are to denote the crank/main bearings are oversized or standard.

 

alright...what does that mean? haha. Is That something from the factory? or does that mean it was rebuilt or something?

 

it from the factory, it means the journals on the crankshaft for either the rods/mains were under/oversized, so if it was rebuilt later.
http://street2mud.com/webfiles/AMC%20Engine%20codes.pdf

look this (1967 and later)

 

oh ok. so basically it was marked so it was clear it needed fixed? and is really no big deal?

 

nevermind, it means in case it is ever rebuilt its known the bearings are different sizes. and still not really a big deal.