found 340 vin #0R3041

That block is out of a 1970 Swinger 340 (late build) all the 1970 Dodge Darts came from the Windsor Ontario plant, which includes the 340 Swingers. I am also looking for my original block but mine is 0R127xxx, i forget the last digits, haha

your block looks like OR304135 to me, those last two digits are really hard to see!