Unless you have the 727, I would go 904, it would need a different driveshaft than the 727, but I would not put a 727 behind a small block. I just changed from a 727 to a 904 and all said and done will have picked up 2.5 to 3 tenths. Now, I increased my flash rpm by 300, in the same dia converter. Both were PTC 9.5” converters. I also changed to the low gear set inside the 904. I also went aluminum for the driveshaft. So it is not just your typical 727 to 904 swap, but no more 727’s for me. Just not necessary. As an added benefit a much lower risk of shattering the drum.