FE build up almost done!!!!

Hey im just finishin up my mild build up on my 68' 390 that im puttin in my 67 ranchero. I put a edelbroke performer intake and cam,hooker headers, 650 holley carb in it and also i put some forged rods and pistons in it with the stock crankshaft, heads and oil pump. My question is that before i tore down the moter i had a slight tapping noise at idle, when i took the stock cam out of it it had no signs of wear but it was missing the spacer between it and the thrust plate as show in the 67' ranchero shop manulle. Is that causeing the noise? is that washer needed? and finnaly what is the proper way to brake in and start that engine for the first time? Hopefully i will be starting it up in a few weeks.