360/904 B&M flexplate

hi has anyone here ever had any problems with the B&M flexplate? Vibration issues or anything? I swapped the 318 out for a 360 using the B&M flexplate. When id the car in gear it would vibrate bad while hole the brakes with car on jack stands but when I let of the brakes and gave it gas it wouldn't vibrate. Anyways I ended up pulling the 360 back out for a rebuild and I'm getting ready to put it back in but I want to try and figure out the vibration problem so I don't have to pull it all back out again. Also is there anyone that makes a 360/904 torque converter?