340 internal balance or not?

I will be using the stock '65 torque converter with 904- I understand converter choices are limited?

Yes, because not only was the snout smaller, the input shaft spline count was also different. Some converter companies could put together a combo with a bigger snout for the newer crank and correct spline count for the old trans/converter. I understand that your budget may be a factor, so best bet would be the adapter ring if your old converter is in good shape.