Think I May Have Found Out Why My 340 Seemed to Idle Rough...

I don't believe those weights are for external balance. I am pretty sure they are there to balance the converter assembly. If it were an externally balanced converter the weights would be on the face of the converter where the flexplate bolts on. The four mounting lugs (one has an offset hole) are used as a refference to position the weights so when installed in relation to the crankshaft they are in the correct position. Plus, that appears to be a high stall aftermarket converter, I have never seen a performance aftermarket converter that is externally (Detroit) balanced. I have however seen a 340 that was rebuilt where someone installed a 273/318 forged crank. That thing vibrated like a washing machine, more so at idle. The 340 forged cranks have holes drilled in the first and last rod throws to lighten them due to 340's using heavier rods.