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

The 50 degrees is not 'power timing' as AJ calls it. It is with vacuum advance added, but that does not happen when you have the throttle wide open.

The are 3 separate advance types that you are working with:
- Initial advance typically in the 10-20 degree range at idle, with the vacuum advance hose plugged. The mechanical advance is 0 at this time. This initial advance is what you set with the timing light at idle.
- Total timing ('power timing') low to mid 30 degree range achieved at somewhere around 2500-3000 RPM, with the vacuum advance hose plugged (to simulate the throttle being wide open). This is the combination of the initial advance plus the mechanical advance in the 'dizzy'. The mechanical advance if stock is typically 20-22 degrees, so if you want this limited to, say 34 degrees, then the initial advance will be around 12 degrees.
- Vacuum advance timing: For the Mopar system, this only come when the engine is revved up for cruise and at light to moderate cruise throttle. It adds to the initial and mechanical advance and can move total timing up into the 50+ degree range under light throttle, cruising conditions. This is an important factor in fuel economy at when cruising.

Get the initial and total in line with what AJ has listed or you have some very real risk of detonation and engine damage.