Here is a tip discovered by my fellow N Scaler Justin as we worked on our layouts. I have used Peco Code 80 in my staging yards and helixes (the old bullet proof syndrome). All visible trackage is Atlas Code 55. To join them up I had fallen back on my HO days and using pliers I flattened one end of a Peco rail joiner and then soldered the Code 55 to the flattened end. A little filing and a decent joint was made but not perfect.
Justin was rebuilding his layout and looking at various types of track and so had Atlas 55, Peco 55, and Peco 80 (which he is also using in staging) sitting around. Looking at the cross sectio of Peco 55 he decided to file off the lower web on one end. This leaves a cross section identical to the Atlas 55. Voila! The other untouched end matches perfectly to the Peco Code 80. We had transition sections between Atlas 55 and Peco 80.
I am using 6 inch sections of Peco 55 since there is a tie height difference and a little shimming is necessary. Take enough ties off one end of the Peco 55 to fit on an Atlas Joiner. Use a good metal file and it takes about 2 to 3 minutes to file off the lower web. I use a piece of Atlas with rail joiners attached as a template to keep testing the Peco to know when I am done. The end result is smooth, seamless, perfect transitions between my Peco Code 80 and my Atlas Code 55.