Cam Interrupter magnet install???

Purchased a shortblock for my 1999 pontiac grand prix gt. 3800 Sll that came with timing chain and gears installed. I verified the timing was set up properly and all that stuff but never thought about a magnet being on my old engines timing gears. Have the engine back together and keep getting code P0341. Replaced cam position sensor. No help because after further investigating I realized that there was no magnetic pick up on the sprocket. Purchased interrupter magnet P/N CSS120. Question is do I have to remove front cover to install or does it snap in from the front through the position sensor hole. Would love some good news because this has been a mess from the beginning.