[dsraven]

any time you are talking mounts be sure to have the bodywork (cab and rad support/rad at least) attached and the steering rack/box in place with steering column at least mocked up and connected as it would be. it saves future headaches. also, aside from what ogre mentions about torque affects, think about how the mounts will affect the exhaust system routing, engine removal/replacement, trans cooler line routing, starter swapping, p/s pump interference and line routing, a/c compressor and line routing, shift linkage or cable routing. think about room for the belt driven fan and hub or at least an electric fan set up and how much room is required for that. if going with a push fan to save room in front of the engine will there be room in front of the rad/ac condenser between the grille for the fan unit. some stuff that you think you will figure out later can turn into a whole bunch of work when the time comes to finish up the "small stuff" and you end up engineering a bunch of changes. think about adjustability for future considerations etc. sometimes a bolt on frame mount for the engine is preferable to something permanently welded in. it can give the engine more room in tight engine bays when removing/installing the engine, later, if the frame side of the mount can simply be unbolted and taken out of the way. if using a through bolt on the engine mount will there be room to get the bolt out without taking a bunch of other stuff off first. when the next job, fabbing a trans cross member, comes around also think about how the exhaust will get to the rear past the cross member, shifter linkages or cable interference, fuel lines, brake master cylinders and boosters, park brake mechanisms etc. how will the trans cross member stiffen the frame to assist the cab mounting flexing issues that come into consideration when the original trans cross member is removed.
anyway, just a few thoughts. sometimes the easiest way to fix a bunch of problems is to do one larger job right away, like a firewall modification, rather than a whole slew of the smaller jobs that only really became an issue because of the modifications required to get an engine sitting in the bay.
sorry, the quick reply came out to be a short story. hope it helps somebody