1984 Mercedes Benz 500sec Timing

My neighbor has the above described car, but not the internet. He has recently changed out the motor, and is having a problem with, what we feel, is the timing.

The engine # is 117 231hp

He has replaced the timing chain, replaced the hog gear and replaced both cams and gears (2 overhead cams).

Car has difficulty starting, and when running, backfires every 1-2 seconds.

The distributor gear has a little play between the gear and housing, the roll pinion gear appears OK.

Ideas? Jim