I'm just curious -- what is the reason for trying to hide the vacuum ports by putting them in the least accessible position (i.e. underside / inside of the head)? They look a lot less obtrusive than those unnecessary in-line fuel filters that so many people use. Are you embarrassed because they are not supposed to be there?
I like the stock appearance on my bikes too, but I cannot imagine the trouble it would be to uncap the fitting and put on a test hose if the port was placed above, and angled toward, the cam chain adjuster housing. Is there a reason to do that?
The Motion Pro Synch Adapter is available almost everywhere, including eBay for $3.99, and it will work just fine. I think anybody would be hard pressed to make them for less than that.
https://www.ebay.com/itm/1736699983...AyO5mu9_KEF-g9n51ZtjHURUehvnZIFYaAlx7EALw_wcB
The hard fibre washer that comes with the adapters work just fine. There is one problem though. The vacuum cap that comes with it will melt in very short order in this application.
My original intention was to leave the adapters in place, and to use the caps that came with them. I soon realized that would not work, so I would remove the adapter when finished synching, and install an M6 button head screw. That was a pain in the butt. I chased down some silicon caps and they work just fine. Silicon caps won't melt, and they come in a variety of colors. My CL350K3 is blue, so I use color coordinated vacuum caps.
They don't exactly stick out like a sore thumb. They have been on there for a long time without melting, or falling or blowing off. I kind of like them.
By the way, anybody who says these are not necessary has never used them. I thought I had my carbs synchronized perfectly till I finally installed these ports and used them. It makes a world of difference!