69 amx 390 point distributor

Bolt it is and don't look back, it will have slightly different vacuum advance and Mechanical advance properties.....but functionally it will work fine.  You can play with the mechanical advance to a point, by buying a Mr Gasket kit for GM/Delco Distributor and changing springs to put the advance "in" at what your engine likes.  You can also buy a adjustable vacuum advance for GM/Delco Distributor and also adjust that with a allen wrench that comes with the kit.  The vacuum advance looks slightly different, kind of a hex shape right before the vacuum nipple....but most don't care about that.  A stock 69 390 distributor 1111473 runs about 26 degrees combined vacuum and mechanical advance......I just ran 2 of them across my Sun 500 Distributor Machine last weekend, just ask AMXTSY.

As mentioned by Ross, the dissy will work fine, though it may not  be ideal for performance. What you need to do is figure out what you have, ie the total mechanical advance and then perhaps make some changes. Look under the advance mechanism of your distributor and there will be a 3 digit number. The last two numbers are the mechanical advance, probably around 30-32. You need to decide if you are happy with what it has or if you want to tune it further.

Most people prefer to have the initial around 10-15 degrees initial and 18-28 degrees of mechanical on top of that, totaling around 34-38 total. As Ross said,  you can use a Mr. Gasket set to change the rate of advance. Probably around 2800-3200 is around where you want it. Last, you can decide what to do with the vacuum advance. Either adjustable or get a vac gauge and buy yourself whatever canister looks like it will best suit your engine. If you decide to fine tune it, lots of people here can help.

Good luck!

Chris