In my experience, anything under 400 is fine with biscuit mounts, they are on ebay NOS and repros. If you are seriously worried about the motor twisting, torque strap the mill and you will be fine. Or go with solids. You could always look for a 73+ kmember and go with spool mounts too.
Thanks for the tip. It’s a 67 dart with a k member from a 72 dart. I might just find some new mounts and try them. The ones I got for the 318 that’s in the car now are very soft. The motor shakes a lot from it being so soft
