Yea. The original 273 adjustable rockers fit no problem, that and a set of comp pro mag (if you opt for roller rockers).
Also the only 340 to have adjustable rockers (from the factory) was the engines used in the T/A and the AAR.
I was running CAT rollers and they fit with no problems. I swapped for the crane ductile iron and 2 of them were touching the baffle on the driver's side. I just smacked the baffle a bit with a hammer and they fit well.