To the best of my knowledge the 340 never came with a 904. I know that the 71 Duster 340 I bought brand new had 727 in it and so has every other 340 I've ever looked at. Send us a photo of the engine side of the 340 converter and also give me the diameter of the converter hub.
This is in a an early A, the 727 doesn't fit without modification so I'm using a 904. And guys this is not a race car and I'm thinking a stock converter will suit my needs just fine, I'm just wanted to find a way to determine the stall.