The front plate needs a major engine teardown to change it- - - -remove the oil pan, the camshaft and the timing gear at the front of the crankshaft and unbolt it from the front of the block. There is also at least two different designs of engine mounts, with different front plates for each one. If the engine you're shopping does not have a front plate, someone has left it off during assembly. The engine cannot run properly without that plate installed due to misalignment of a bunch of parts at the front of the engine without it in place.
Jerry
