LA small block timing is suddenly way off

Here is a quick check for cam timing.
-Crank at #1TDC: thats proven TDC,.. as piston stop used.Drivers side valve cover off.Plugs out. If on compression stroke, rotate 1 full revolution.Now while observing the rockerarm motion at #1 cylinder,reverse rotate the crank to about 10*advanced, then forward rotate about to about 10*retarded. Repeat several times. If cam is anywhere near correct you will be able to observe the valves going through split-overlap, the time when both valves are slightly open, the one closing and the other opening. A sloppy chain or a large cam may require slightly more degrees of rocking. The point is,split overlap with a good chain should occur at or near the TDC mark( probably within 5*).Are you starting to understand how important the TRUE TDC mark is? A jumped chain is easy to spot this way.
-If your chain has jumped, replace it with a double roller set. And I have used the Mopar tensioner to good effect so recommend it as well. Those chains go a long long time.
-and after replacing a chain, the dist. will have to be retimed.