Your mechanic is right there are two little tabs welded on the bottom of a manual crossmember that are'nt there on an automatic crossmember you can just bolt on the manual mount to the top of the auto crossmember without the lower tabs but it will be very flimsy, I just went through this whole ordeal, luckily I still had my manual frame in the back yard and just cut off the old tabs and had a buddy weld them on

Thanks EdMan for the confermation. I like my mechinic he seems to know what he doing.