Two piece mounts will NEVER be as rigid and solid as a one piece plate................doesn't matter if you tighten the bolts after every run

A BBM does not have bolt holes in the bottom of the block to help hold the plate in place, like Chevy motors do, so clamped behind the water pump mounts is it, that's all you got. Gives a scissor effect as MrP says and it always will. The holes are never precision, so they come off and put them back on, they may or may not be in the same place. If you ever need a screwdriver to line them up with chassis.........SOMETHING moved. May not be big deal for many, but the two piece ones do move around