The leak is coming from either the cam or the EGR hole on the front R head.
the EGR hole is tapped into the exhaust port on the head, so that should not be it.
it certainly could be the cam seal. when you set them they should not be set deep. just flush with the service i think. when / if you re-locate the heads check the cam shaft for scratch marks.
pull the right cam timing cover and see if the oil is coming from behind the sprocket.
if no, it is probably coming from the oil pump / crank seal.
i had a 95 that popped out a right side cam seal. i didn't do the timing belt job so i'm not sure if it had been replaced but i think i was. so it was probably 40k old. i have no idea why it did it other than age. but i replaced the pcv and the hoses around it just in case.
swapping the heads is going to be a pain. you will have to replace the the cam seals.