71 LA 340 timings moved!! how?? looking for help

With no load on the engine it is common for the engine to want between 50 and 60 degrees of timing at cruise rpm. So you can't hurt it with a true 40/50 after 2500 rpm with no load.

This is also why the Vcan will someday have to be re-connected. The engine wants what it wants, and if you don't give her what she wants,she will complain about it, just not as loudly, or as often, as when it detonates.

I don't know what the big deal is, just put the power-timing back to where it's supposed to be, tighten the clamp and if it idles ok you're done. Then index the D housing to the block with a chisel mark,and keep your eye on it.
I mean 50 less 32 is 18 in the D. If you reset the power-timing to 34 then you will have 16 initial, And that is pretty close to perfect.
Now if it comes in too slow or too fast, well then some springing is in order. But your test shows only 6 degrees added from idle to 2500,and only 10 degrees added by 3500,and only 18* by blipping to guessing 4000; so that looks pretty tame.The curve appears to be pretty safe for the combo.