Will my engine fit? Help!

Fitted airfilter just it started but kept spluttering when I revved it and the oil pressure light stayed on but to be fair it's freezing cold here at the moment and after a couple of minutes oil light went off and the chugging stopped.it settled down to 1200 rpm but is still a bit lumpy isn't running smoothe and exhaust gas smells strong

spluttering could be a missfire, have you put new cap, arm, leads & plugs on it?

Yeah apart from plugs might check them tonight,I took it up the road last night and let it warm up it drove fine but just is a bit rough on tickover