Molasses attack

I have been subscribing to your magazine from the first issue. I still enjoy it and look forward to a good read every time. I have some experience with molasses de-rusting. A friend of mine used it in an old bath tub to de-rust panels from an MG B restoration with great success. I made a mix and it worked very well if you leave it about two weeks. BUT !!! I then put in the cast iron barrel and head off my New Imperial, which is a 1939 model 110 500 cc. When I took them out they were black and slimy.