I understand your concern. Engine rebuild is EXPENSIVE!
First off, Recurving the stock distributor is a piece of cake!
Motorcraft made their distributors VERY easy to tune!
Detonation is going to happen with both ignitions if they are not tuned correctly.
You will stand a better chance with the stock Ignition and the cap, rotor, coil, plug wire upgrade.
This ignition system is tuned specifically for your vehicle, and as long as you keep the stock amount of initial timing, you shouldn't have any problems.
Detonation is going to occur with any ignition, but will be lessened if you are SURE there are no vacuum/ air leaks, and the mixture isn't too lean, and the ignition TOTAL timing isn't too far advanced.
(If you have detonation now, going to a GM style HEI is a good way to have even more, more advance quicker, less spark energy, = More detonation...)
If I had an '86, the first thing I would do is double and triple check the for intake leaks, EGR leaks, ect.
The next thing I'd do is make sure the idle mixture is rich enough, and evenly balanced.
If I had detonation problems in the past, and I was going to use the same basic parts, I'd spring for a Detonation Sensor ('Knock' sensor, dash mounted).
This will let me detect even very small amounts of detonation I couldn't hear with the plain ear, or detect on the spark plugs yet.
MSD P/N 8964 $142.95
A good way to determine if your fuel mixture is correct is a Rich/Lean indicator.
You install an O2 sensor in your exhaust collector, and a dash mounted display will tell you if your mixture is rich or lean. (lean will cause detonation)
MSD P/N 8933. $149.95
You can control your timing WHILE DRIVING, up to 15 degrees with a dash mounted knob.
MSD P/N 8680. $92.50
MSD 6A module is always a good investment.
The DUI and the Motorcraft/ DuraSpark ignitions are both Inductive.
The MSD 6A module will upgrade you to a Capacitive Discharge Ignition (CDI) system, and you can use the Stock distributor. (that will save you a ton of money!)
This one very reasonably priced upgrade will increase your useable spark energy 100% to 1,000% !
There is no better bang for your money.
MSD P/N 6200 $132.95
I personally think your money is best spent on the 6A module and the knock sensor if you have detonation problems.
(prices are from the Summit catalog http://www.summitracing.com
So many cats, so few recipes...