First re swapping around a couple of injectors - you live and learn. Best to check out the easy/cheap possibilities first and diagnosis is important.
Secondly, if it were number two clearance, how does that pot compare with another? If clearances are all the same, it ain't likely to be the problem.
Piston slap usually goes away as the engine gets towards working temperature from cold, so would be much more noticeable at cold start up. I would be asking an engine reconditioner the question. It could be a piston pin and that is usually a distinct rattle rather than a knock.
While it is apart I would be checking ring to groove clearance and ring end clearance for wear. Clearances for pistons and rings are usually quoted as a minimum and maximum per unit diameter for most all engines. I always remember, from way back when, ring clearance was 2 1/2 thou per inch of bore but I now use metric as they are so much more universal and generally easier.