What will cause slight miss idling on a 65 170?

No need to go that complicated. This has always worked for me.
OK so the piston pairs on your /6 are 1+6, 2+5, & 3+4. Crank the engine by hand until the valves on #1 cylinder are overlapping. (i.e. exh. Valve just closing & Inlet valve just opening) Adjust the valve lash on both valves of cyl #6. Crank the engine once again by hand until the valves on #5 cyl are overlapping & adjust the lash on both valves of cyl#2. Crank again by hand until the valves on cyl. # 3 are overlapping & adjust the lash on both valves of cyl. # 4. Follow this sequence in the firing order (153624) & you wont end up hand cranking the engine a thousand times. Take your time and set the lash accurately.
Like I said it has always worked for me & the way I was taught many years ago. ( Just after ww1 if I remember correctly):thumblef: