LOL.... I completely feel your pain, I have been at war with the Cosmoline on my car for weeks now. You are right the stuff is beyond resilient. Fortunately my car is completely torn down to pieces and I have access to a parts washer but that stuff is still fighting us tooth an nail. My old front LCA's and springs were so bad that is seriously looked (and felt) like they were covered in cement! I have not got around to it yet but when it comes to the engine I have already bought a number of different Dremel brushes ranging from Nylon to Brass and
I think those in conjunction with some of the solvents you have mentioned will hopefully do the trick in getting all the Cosmoline off the block. That said a Dremel and in your case with the engine in the car a 225-01 Flex Shaft Attachment (
http://www.amazon.com/Dremel-225-01-Flex-Shaft-Attachment/dp/B0000302Y8 ) might be your weapon of choice to take the fight to the rest of the Cosmoline in the tight spots.