He is wants to run the factory 68 4 speed cam. Assuming he has the 340 rocker system all he has to do is inspect the rockers and shafts, drop the pushrods into the lifters and bolt them on.
Not saying you are wrong, but how much will he gain with perfect preload after spending how much money and the time to do it correctly?
Many of these replacement factory cams are reground from cam cores not having the same base circle . You should never think just because it has the same lift and duration that they are ground off of the same base circle.
Now if he just happened to locate an original Chrysler cam from 1967-68. Then you can just bolt on the rockers . Providing you are using heads that have never been cut or has block that was never square decked.