You are in Canada,

I believe YS 110 should be good with Zen. I am just not sure about the Macs products' header parts since I have not tried. I am using Hatori header available from Central Hobbies, RadioSouth etc. No idea where you can find in Canada.
Central hobbies also has new NMP header for YS 91~ 160. I will probably get one to try out.

For a 2-stroke engine, Send an E-mail to Karl Mueller ([email protected]). He makes great wrap-around headers for side exhaust engines for rear exhaust applications. I am using one of his header with 91Fx in a JR Propo Explorer 90.

Good luck.

Ihncheol Park