I suggest using a Walbro carb over a Zama, and it must be a two needle carb. Many of the newer carbs don't have dual needles for adjustment of both high and low mixtures, and having this is a necessity. The carb bolt hole spacing on all the carbs are the same, so no worries there. The pulse hole orientation can be changed by grinding an annular groove in the carb adapter to line things up, so this is no problem either. Many carb adapters already have a groove in them, so mounting the carb either upside down or right side up is possible with no mods. In any case, an external pulse is also very easy to set up.

What you want for that engine is a carb with an 11.1 mm venturi. The Walbro carbs have a number cast into the carb throat, such as a "24", or "32", etc. This is the size of that carb's venturi in 64ths of an inch. (24/64" for example) What you want for that engine is a "28" carb, which is a 11.1 mm venturi. If you have the carb number, such as WT-317 for example, you can go to the Walbro website and look up the venturi size.

With a larger 11.1 mm carb, and if you gut the muffler of all baffles, screens, etc. and provide a much larger outlet, you will see a nice large power increase. You are correct, the Echo engines are very good. MUCH higher quality than the current Chinese engines. The Echo engines, like Stihl, are among the best.

Good luck and have fun,
AV8TOR