a pop sound thru the exhaust or intake ?
it could be a jumped timing chain, if thats the popping sound im thinking of...
its a fairly easy d.i.y. project,
a good half day if you have some mechanical knowledge
a quick way to check timing chain slack on that high mileage of a motor is to grab the harmonic dampner ,
rotate it side to side, and you will feel the slack in the chain...
especially if it jumped, probably about $30 in parts, roughly
check your ignition timing, since the distributor was replaced,
maybe its retarded/advanced too much