Rear tire size needed for 340 stroker?

Trying to figure out what tire size to use is just one of many components that need to be figured out when building/setting up a car. I'm not saying that you're putting the cart before the horse but all of the sub-assemblies should be taken into consideration before making changes/purchases (to eliminate wasting time/money). Build it all on paper.

Btw: A 275/60/15 should easily fit in a Duster rear well even on a 15x8 rim with the right back spacing. Just remember to measure both sides since Ma wasn't known for perfectly centering her rearend assemblies. As 72Val said, if there was a minor clearance issue, you could sue the offset hanger/shacke kit and get an extra .8".