This forum [ & many others ] are full of stories like this. New cam, & it wants [...and needs ] more timing at idle to run as well as it can.
In this case, it sounds like advancing the dist to provide the additional advance has caused the VA unit to limit dist movement.
You do NOT have to remove the dist. If you rotated the dist one full turn, it would rotate 360*. Eight cylinders, so you only need to rotate the dist 1/8 turn, 45*.
Rotate the dist 45* in the direction that gives VA clearance. The easiest way to do this in situ is to measure from one of the plug lead towers to a convenient spot, say brake booster edge. Decide which direction the dist needs to be rotated. Rotate the dist 45* until the next-in-line plug lead tower is in the measured location.
Now you have to move the HT leads. They get moved in the opposite direction to what the dist got turned. If the dist got turned CCW, the leads get moved one position CW. Using this as an example, find #1 plug lead. Remove it. It now goes in the tower next to it, going CW. Continue on until all the leads are done.
Start the engine & check timing.
