The only reason to not run a vacuum advance on a 427 is to look original. I am guessing that Ford did not put vacuum advance on the 427 and 289 HiPo engined street cars, is because these engines came with dual point distributors. My guess is the dual point distributor did not have enough room for the vacuum advance.
You already have a MSD distributor. I would keep it and tune it. I like the black bushing to limit the amount of ignition advance and then set the idle ignition up around 20 degrees initial. I also like using the blue spring and the light silver spring. These are the two lightest springs. This will give you the second fastest curve. I would prefer to run the fastest curve, but the idle is a little rough because the springs are not quite strong enough to hold the timing constant. The important thing to remember for most 427 with aluminum heads with around 10:1 compression is to not go over 36 degrees total at wide open throttle.
For your MSD distributor, I would also recommend running an MSD 6530 or something equivalent with a MAP sensor. As has been pointed out by several people there are lots of advantages to running a manifold pressure referenced ignition advance system.
1. cleaner running spark plugs,
2. cooler running engine and exhaust system (cooler side pipes)
3. better fuel mileage
4. better throttle response
5. smoother running engine, especially at idle
Here is a link on ClubCobra on how I was able to solve some of these issues with a Weber equipped engine, with an MSD 6530.
MSD 6530 with throttle postion sensor
The instructions also say you should lock out the mechanical advance. I wouldn't but you will have to account for the mechanical advance in your programming. This will help with rotor phasing...
I also suspect with more ignition timing, your engine will calm down somewhat at idle. Easy to check...
And yes your engine has a big cam.
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