I suspect you fell lucky with the left side. I always need to take the headers out of the collector to get them mounted in place, but then my collector is outside the car so the headers are much longer and include the 90 degree bend.
Take the headers out of the collector and very loosely bolt them onto the engine. Slide the collector onto the headers, maybe use some copper grease and when everything is in the right place, tighten up the header bolts.
That always works for me.
Paul