67' 318 crank in a 69' 340

Back when Sears used to sell crankshaft kits, I spun a bearing in the 340 that was in my Duster. I was still in high school and didn't have much money to spend so I pulled the engine out, turned it upside down and removed the crankshaft. Turns out it had two 318 rods and six 340 rods on 180 out throws. I think number 2 and number 5. I put the cheapo Sears crank kit which was cast btw in it and ran the fool out of it. I never noticed a vibration. I turned it 6 grand regularly. I don't think using the 318 crank will be a problem regardless of whether you balance it or not. IMO