The block would have to be a 109 block. The 84-85 heads are not threaded in the block enough and the pre 84's are a completely different deal all together. You have to have a 86-87 109 block. You can get a 109 block out of a natural asperiated car, but you would have to drill a oil drain tube hole in it and tap it. If you are going for cheap that is the cheapest way.
First and foremost. Is it an 87 engine? It should be stamped as a "109" block. Next make sure it has a oil drain tube hole drilled and tapped on the top left of the block.. If that checks out then you are doing good. If you want, give me a call and I will walk you through. 803-492-3518