have changed a engine in a mates car and we can't get it to start.

It defo has fuel and spark but just turns over. Have tried turning it over without plugs in for a while, in case tappets are empty (not sure if it applies on these but tried anyway). The plugs have loads of oil on after trying to start it, could this point towards a issue with the new engine? Thinking its lack of compression due to rings maybe? Mate got the engine, but doesn't really know anything about it.

We have been trying to start it with only the manifold and cat/down pipe on, but thats not gonna stop it starting is it?