The 540 elans yamaha cousin.... You should twin carb this one. The 540 motor does not run up to full potential with a single and no air box.
Also keep in mind, the Yamaha pogos can be difficult to find parts for. The Vmax 5/600 pogos offer more travel than the Phazer II/SRV/80's Vmax pogos but there are no replacement struts available. There are replacements available for the Phazer style. The Ovation and early Phazers have a completely different style strut that is absolut garbage in my opinion. Avoid those. I would either look for a really nice pair off of a Vmax 5/600 or Phazer II for ease of things.
Does the Enticer have a round crossmember on the front of the bulkhead for the front suspension?
This thread may be helpful when you get farther into the front suspension swap if you decide to stay with Yamaha parts:
http://www.totallyamaha.net/forums/showthread.php?92300-Another-Yamaha-in-the-stable