I don't run a motor plate but do have solid engine mounts but use a stock style trans mount because if you use a solid trans mount with solid motor mounts it can break the trans case or tail housing from chassis flex. It doesn't take much flexing either.
I will eventually go to motor plates and they are supposed to be mounted solid to the chassis to help tie the frame rails together to stiffen the car. Plus usually you want to run a mid plate if you use a motor plate because of the stiffening I mentioned. Front engine plates without a mid plate put a lot of load on the bellhousing to block area being the distance from the block plate to the stock trans mount is so far apart.
Chuck