I would make sure timing is 100% and then do a compression test both wet and dry. Have a look at the spark plugs, are they oil fouled? Take note on which cylinder each plug comes out of as it will give u an indication of what is going on in each cylinder. If the engine overheated that bad it will damage the piston rings ( the heat causes them to loose their spring tension and not seal) once the head has been repaired the next weakest link could be the rings/ bores. I say this as I have seen it before. If compression is good move on to something else