There will be a distribtor hold down with 1 bolt were the distributor center shaft flange goes down into the engine block usually you only need to loosen that bolt a little bit until the distribtor will turn. To see the hold down and its locking bolt you need to look under the distribtor cap / wide part of the distribtor body to the center shaft. Picture of a 1965 Ford 200 Six engine assembled showing the stock distributor installed.
http://1.bp.blogspot.com/-4yUKrlTv540/T69874TcRxI/AAAAAAAAAOc/5-q_MNg-Tys/s1600/IMG_1881.JPG
In this 1965 Ford 200 distributor close up shot you can see the block flange that the distributor hold down pushes against to hold it from moving, below that is the part that fits into the blocks distributor hole. After the timing is adjusted and set you only need to snug down that locking bolt it's not nessisary for it to be torqued down a very much.
https://i.ebayimg.com/images/g/OIAAAOSws2RcSlX8/s-l640.jpg
Best of luck