Which FE is important to know, because there are some
oil design differences. Certain engines require a special cam bearing. Much to know about the
oil system improvements that should be done. You should drill a bigger hole somewhere around the
oil filter on center oilers.
Much to do about the intake and head to get a proper fit. Depending on cam lift you may need to relieve the push rod holes to prevent contact. A cast iron intake is heavy and makes working with it difficult. Getting all the ports to match to the head, the dizzy in the right spot, and getting surfaces mated is important, to prevent leaks.
If the skirt is drilled for main support bolts, that is another area to know. The rear main seal was designed for a rope seal and therefore did not require much precision. It is a real pain to get a modern rear seal to actually seal.
Let's see there is some strange thrust bearing thing with the cam, if memory serves. Oh yea the oil pressure relief system was quite unique.
I probably got some things wrong and left some stuff out, cause I never actually built one, but I read a couple books on them maybe a decade ago. I suggest you do the same.