360 engine vibration

Checked the invoice and it says BM 10236, also a stroke of luck since it is fitted now is that I took a photo of the plate and fitting instructions before fitting and these confirm 10236. Strange thing is I noticed no difference before and after fitting the BVM flexplate, maybe the vibration this is meant to eliminate happens at higher rpm or frequency? Mine is still at about 1000rpm plus.

I need to take the front pulley off and check this is the correct balance for a 360 LA engine. is there a difference between magnum and LA front harmonic balancers?