"I am wondering about increasing the stroke with longer rods and shorter pistons"
Stroke won't change with swapping rods/pistons, it's the crank that determines stroke. If you use longer rod, piston speed goes down though and there is less side load on the pistons, which is good. Stroke will remain 80mm.

"I have the plan to keep the original 44mm intake valves and going with 40mm exhaust..."
I'm no B30 expert, but I don't believe 40mmm exhaust valves would be necesarry. I believe it's mainly the port that will limit exhaust flow, not valve size. Going to 40 mm will leave you with a shrouded valve.

"...and a K cam. Would I possibly need a hotter cam than the K?"
I think the K would be a fairly good choise, perhaps retard it a few degrees. I wouldn't go any bigger though.

"I would love 300 miles from the tank. Is this out of the question with these parts?"
How big is the tank? I reccon it's doable, but it's all about how you actualy drive it. If you build the motor correctly you might even get extra mpg if you don't actuall use the extra power.
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P131, '65, B20B+M47+DGV. P131, '69, B20E+AW71L+LSD. (www.tinustechniek.tk)