hi, is the gearbox beam/crossmember the large flat plate i can make out in the pics? if so are you adding anything else to the plate to stop it flexing up and down with the weight of the engine/box? we did one just like this on an 82 monte carlo and it flexed up and down like you wouldn't believe. we put a piece of flat bar on edge front and back of the plate to make it an i beam and that sorted it. we were amazed that plate that thick could flex that much but it did.