Engine Block Cleaning HELP

[tgeib64]

I just bought a 93' 240sx with a red top sr in it, and it has some oxidation on the engine block. The engine is currently still in the car and i was hoping to be able to clean the block with out taking the engine out. Ive done my research and what i found is some people were using gelly paint removal. I was wondering if any one has tried this and if it works or not and or any other methods that may help clean it. Thanks for any helpful replies!