The Tak clamshell CAN fit a modern dovetail - either Losmandy D section or Vixen V section. Many makers make a Losmandy D plate with specific Takahashi mounting spacing and rebated circular section, or you can simply use a Vixen dovetail with the bolt SLOTS like this one:
http://myastroshop.com.au/products/d...p?id=MAS-096I3
I have some customs made Tak clamshell allen head screws if you need some - they fit the Tak clamshell holes precisely, and then step down for standard 6mm slots.
You can also drill your own holes in a standard V plate or D plate to save some money.
Here's a Google link to images of the ready made plates:
https://www.google.com.au/search?q=T...w=1536&bih=759 - take your pick!
Here is the Farpoint:
http://www.buytelescopes.com/farpoin...il-plate-short
As to 200mm rings, Parallax in the USA make them - they are a couple hundred dollars.