What ever you deside to use. Do not rely on the factory motor mount ears . They stress the block and the 340 , 360's cannot take it. One of the reasons they moved the left side rear ears forward. Always use a motor plate or turn buckles for added support. This is the weak link and why you always see one of these two cylinders fail under torque from flex. Seen many pistons go through the wall on these two cylinder and break the rod. The rod is always blamed but it is the block. One of the reasons Chassis cars use front and mid motor plates. Good R3's don't even have mount ears.