The 10237 B&M flex plate fixed my problem. Car rides like a new one now.

This may also help me fix the same kind of issue I've had with my 70 440+6 car. It is externally balanced as well and I would bet 35 years ago, someone put the wrong torque converter in it with no weights. Inspection cover coming off that this weekend to verify my suspicion.

Thanks everyone for the help !!

1968 Barracuda Fastback 318-2BBL 904 2.76 Frost Blue Survivor
1970 Roadrunner 440+6 BBL 727 AT 4.10 SG Dana Blue Fire Metallic
1971 Cuda 340-4 BBL 4spd 3.91 SG Curious Yellow
1972 Barracuda 318-2 BBL 904 AT 3.23 1 Legger Tor Red/White Vinyl Top
2007 Dodge Ram 1500 5.7 Hemi AT Patriot Blue
2011 Dodge Challenger RT 5.7 Hemi 6spd 392 SG Triple Black
2014 Dodge Charger RT Max AWD 5.7 Hemi AT 305 Billet Silver