It's a little late for Jackshafting now, you want to do it with a new clean motor before you mount it and the rear sprocket.
Are they worth the extra $200?
Every penny of it, especially on a gutless stock 48cc, you'll beat a stock 66cc direct drive off the line and run with them flat out.
I also prefer internal shifters, just one rear sprocket keeps the chain tight and quite.
I have built a lot of shifters, you can see some of them here.
If you have the budget get an SBP Expansion chamber and Iridium plug as well and you'll leave those stock 66's in your dust.
Zoom Zoom Baby ;-}