A999 Transmission mated to a 73 340 motor

Hello,

I have a 65 Dart and I swapped the /6 in for a 340 motor I had in my garage from an earlier project.
The 340 is a low compression '73 externally balanced. It has the proper balancer up front.
I installed an A999 behind it with neutral TQ and a B&M flexplate for a 340. This flexplate is meant for a A727 behind a 340 according to their website.
Do you guys know if bolting this flexplate to an A999 is a problem? The bolt pattern is the same.
I drove the car around the block and it seems it has some vibration. Just trying to eliminate some of the gremlins....

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