Timing Curve on 360 in an RV

How can you know what the engine wants for Low-load and PT timing.
That 's easy, with a distributor. AFTER the Power-Timing is getting close to finalized, AND the Idle-timing is fixed, THEN;here's what I do;
In Neutral, brakes applied,
I crank the engine up to ~1800rpm, and just start cranking in more timing, while simultaneously keeping the rpm at 1800. When I think I'm close, I begin being careful to only advance small amounts, always keeping the rpm at 1800. When I get really really close, more toiming will slow the rpm, and then I know I am too far, so now I check the timing with a light, read the number, and back it up 3*. That will be my cruise timing maximum starter target.
THen I move up to 2400 and repeat. Then 3200 and repeat. If a standard trans, then 1400 and repeat. Then I return the Idle-Timing to as I found it.
Now I have three or four data points which I can plot on a graph, and connect the dots, averaging as I do. From that line, I then subtract the Power-Timing, to arrive at what the Vacuum-advance program needs to approximate.
If you change the Power-Timing, You will then have to revisit the Vacuum advance because I only built in 3* of cushion.
Furthermore, the above was a MAXIMUM, NO-LOAD curve.If you were to install this curve you might find it pings mercilessly when switching from PT and going to the Power-Timing curve. Therefore, I recommend to take out 6* from the entire plotted line, and again
sneak up on it, little by little,