rebuild a 420

howdy guys..I have a 1987 420 with 210k miles..it is smoking at idle as described is my earlier posts..so I decided to pull heads and have them rebuilt..question now is .. is it terribly hard to put rings/brgs/seals in these motors ?.... is there parts that should be replaced if i go that far that might be overlooked?..anyone that has pulled one of these motors down want to reply would be appreciated ..thanks