A regulator can go before or after a rail, it is up to the installer or the design of the kit. The regulator works by bleeding pressure from the fuel system. You can tap into the fuel system anywhere you wish to feed a regulator. Ideally the regulator is spliced in close to the rails or off the rails, so that it is regulating true rail pressure or as close as possible to rail pressure.
In CJM kits with billet rails, the regulator is after the rails. In CJM kits with stock rails for VHR, the regulator is before the rails. This adapter is used to splice fuel for a regulator off the fuel rail inlet tube at the front of the engine :
https://cj-motorsports.com/products/...p-4-way-2-bolt
Fuel dampers are highly recommended. The more the merrier, but we have found in most cases that VQs with a damper on each rail do well enough without the 3rd one on the feed line.
https://cj-motorsports.com/products/...output-fitting
drop down selection 320.0086 is an adapter that allows -6 connection to the stock fuel pipe.
https://cj-motorsports.com/products/...-nissan-2-bolt
this is a real simple adapter if you want to replace the damper with a AN adapter to make a new feed line and dont need the outlet for a regulator/return like the 4-way adapter I linked above.