Good questions!
Chrysler pioneered the VR (variable reluctor) magnetic triggering system in the 70s and in their automotive line.
VR is a tried and proven system, and very seldom lets us down in either Automotive or Marine.
Depending on what Ignitions you now have, they may be VR.
Mallory's YLM series is VR, and does use mechanical advance, as likely do your 1979 OEM systems.
The Mallory YLU is photo eye triggering.
If you are OK with photo eye, the advancing system will be similar to the YLM.
(VR is magnetic.... photo eye uses an infra red light beam)
The weak link with any mechanically advancing type ignition system
as they age, will be a worn advancing system......, ranging from shaft/bushing wear, flyweight return spring failure, sticky components, etc.... any of which may cause the advance to no longer meet the OEM curve/limit.
(one of my pet peeves with installing a conversion kit, without having the curve/limit checked on a Distributor Machine
)
Now we have EST (electronic spark timing) systems to look at, such as the Delco Voyager, and several others.
Most of these use "Photo Eye" triggering.... but with NO mechanical advance.
The advance is accomplished via an electronic module.
(if you are OK with turning over your advance to electronic circuitry, then this may be for you!)
My personal choice would be to stay with mechanical advance for these older engines.
Then you'll have HEI (high energy ignition) to consider. I believe that most of these will be photo eye triggering.
Advance is again accomplished via an electronic module.
IMOO, HEI is unnecessary for our lower RPM cruiser engines..... your call on that!
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What ever you do, find the progressive advance specs for these engines, and the limit RPM at which the advance is "full in".
Then after setting BASE, increase RPM and strobe your timing marks and jot down the numbers at 200/300 RPM increments up to approximately 3.2k rpm.... (or where the advance has reached "full in").
Compare these numbers to your OEM ignition advance curve/limit.
Make adjustments accordingly.
Incorrect ignition advance will hold back performance.
The ignition must give the correct curve and TA, for any power to be had.
Remember...... a TA number is worthless without be accompanied with an RPM.
Example ONLY: 26* total advance @ 3,200 rpm
So when you check TA (total advance), make certain that it is Full In
no sooner, nor later, than what the OEM specifies in crankshaft degrees.
Do this, and you'll take advantage of the correct ignition advance (= performance), and reduce the risk of Marine Load Detonation Damage.
Edit: you asked about VR triggering and how it works, so I'll nut shell this for you:
The reluctor for a V-8 has 8 precisionally machined magnetically charged points to it.
It rotates one half engine RPM.
As each point passes within a pre-determined distance from the sensor unit, the sensor causes the circuitry to collapse the coil's primary field (the triggering event), sending a secondary high voltage spark out via cap/rotor/plug wires etc.
Basically, it is performing the same task as mechanical points, but much more efficiently and precisionally.
Triggering is not as greatly affected by high RPM, and wear is a non-issue.
Dwell Angle (aka coil saturation) is controlled by the sensor to reluctor tip clearance dimension, and will be "Pre-Set".
