I have a 73 340 external balanced, I put on the solid sfi flex plate for external balanced engine. My question is do I use the weighted torque converter with this, or does this flex plate take place of having a weighted converter.

Unless the flexplate is cut out or weighted to balance,you would still need the counterbalanced/weighted converter.
RT

I would do whatever you need to do/swap to be able to run a "regular" internally balanced type converter. that way you can get a good aftermarket converter right now & if you swap it out in the future you dont have to deal with the balance issue & I think the HP aftermarket ones are internally balanced??

There were 2 choices of the sfi flex plate, one for internal balance and one for external balanced. The difference between the two is the external balanced one has a moon shape cut out whereas the intrenal one has no cutout.

The aftermarket flex plate with the cut out is so you can run a converter with out the weights. The factory puts the weights on the converter and uses a standard flex plate.

Thanks for the help

FWIW, that year 340 has a unique balance.

Does B&M have more than one external balanced (cutout) plate for the 904 and the 727's to deal with that? (2 each)

https://www.summitracing.com/parts/bmm-10235/overview/make/dodge

they only show that if fits a 727....but

this is the 73 340 externally balanced flexplate that needed to be used with NON Weight converter...

The damper needs to for an Externally Balanced 73 340 crankshaft also..if you do not have the original one ..Professional Products Makes a multi use balancer that has the correct weight that bolts on to the damper to work on a 340 cast crank..

the externally cut out 360 balancer does not interchange with the externally balanced 340...on either end of the engine. balancer or damper.