Rattles like a diesel from valve

Noise is in valve covers at idle, louder on left than the right. Haven't driven it due to noise. Fairly easy tear down and assembly, I guess it's always possible that something was installed incorrectly. I pulled left bank valve cover and it seem to me as if there is way too much clearance between lobe and lifter cap. Racking my brain on this one. Thanks for your input.

Maybe it's not as easy as you think!

Oil level is full.

Thank you for your help. I pulled the timing cover off and discovered that the bolt had just barely loosened up. Tightened it.... No rattle anymore. Now! It started right up and ran very smooth, after a couple of min it started to chug at idle and the shop filled up with exhaust smelling like rotten eggs, as soon as i touched throttle it died. Won't start and if it does, if i move throttle it dies. Also to note that it wouldn't start wot, if I let go it would seem to want to catch, and at times starting but just chugging. I tested mass, tps those seem to be fine.

REMOVE O2 sensors and see if it starts---IF it does (check plugs for fouling PRIOR to trying to start!!!!) , then along with failed head gaskets , it also ruined the converter(s). Been there , done that , with a Mazda truck , brought to me in pieces years ago , No info on WHY the rebuild , and after together , same stuff , started and rqan for about 3-5 minutes , then after that , spit back throug carb(YES - it was an older one- with 3 converters) front 2 cats were clogged pulled sensor to allow to 'exhale' and it started right up(after pulling cover and re-checking my timing etc. twice!!)...good luck. ....AGAIN--- you'd be surprised at what a simple vacuum gauge can tell!!