Good to see someone doing something a bit different,

As far as the engine mount goes i think you've got it bang on as this is the exact configuration as the zetec se that you had in the first place, i.e. 1 rear lower gearbox mount, 1 upper gearbox mount and 1 engine mount. As its the lower gearbox 'dogbone' mount that restrains the engine from pivoting about the other two mounts, rocking should not be an issue unless the engine is going to be very wild. I think the only thing you will need to consider is making sure the mount that you are making doesnt get in the way of any ancilliaries or the head itself etc.

Hope this helps

cheers

Alan