Large RPM and Vacuum drop when shifting from park to gear

Are you sure you have located TDC accurately and can actually check where your timing is? Best idle is likely way too advanced unless you have already shortened the mechanical advance curve in the distributor. Sorry if this has been already covered in the thread ;)

But to answer the question you asked, you could either move all the wires one hole over, and rotate the distributor 45 degrees, and go from there. Or pull the intermediate shaft up, rotate it one tooth, and re-engage the gear.

I haven't checked if TDC is marked correctly. I don't own a timing light (yet), should have it by monady or tuesday. I really don't know what my distributor curve is, since I bought the car as is and the previous owner also bought it in the state it is now.

To clarify, one of your suggestions is to move the wires on hole over COUNTERCLOCKWISE and rotate the dist 45 deegress CLOCKWISE.