Don't quite understand what you are saying.

If you are blocking the flow completely to the heater core and return to the mixing valve you will overheat the rear of your engine unless you have done a reroute.

Sorry should have elaborated. 949 reroute on my car. Heater core doesn't work so I want to take it out of the loop. Seems as though the issue is replicating the restriction that the heater core puts on the cooling system so that there is enough flow through the system while the thermostat is closed. Correct?

This is accomplished by either drilling holes in the thermostat, gutting the thermostat or looping the heater inlet/outlet lines with some sort of smaller pass-through inside the hose. Correct? If so, which way is preferred.

Hope this makes fore sense.

The preferred method is different based on intended use. Of the three methods, looping it back to the mixing manifold will provide for the shortest warm-up time to optimum operating temps, which will help your oil warm up quicker. Cold oil = poor lubrication.

Do the above and if your thermostat is mounted in the rear of the head, leave it alone. If it is mounted in a line going to the radiator, drill a small 3/16 hole in the flange so that the warm water gets to it to open it when up to temperature.

So from my understanding if I want to delete the Heater core is it better to loop from my begi spacer heater barb to the mixing manifold or to the upper radiator hose?
And would I need a restrictor if my T.stat is in the back of the head?

Loop your heater hose to the mixing manifold or lower radiator hose if you have eliminated the hard line.

You should not need a restrictor.

If your thermostat is in the back of the head you should be good with the little "jiggler" on the tstat flange pointing upward.