Where can I buy a reliable remanufactured 318 for 1971 Duster?

i've had good luck with jasper and ATK and their warranties are pretty decent. the only issue is that most all of the long blocks they sell are smogger, so you'll need to seal up the air ports in the heads.

if i was in your position, i'd go about it one of two ways. order up a short block and then have the heads done locally-- if they are still in decent shape. and then upgrade the timing chain and slip in a better cam and lifters.

if the heads need more than a bit of freshening up, then i'd order up a long block and call it done.

it's easy to get sucked into the upgrade vortex at this stage of the game. but if you keep it basic you should be able to avoid a bunch of down time.