Always stronger to glue it together and "bandage" the joint with fiberglass. There are a few models i have seen that do not require the wings to be permanently joined and I have gone ahead and done this. Most notable was the earlier version Tower Trainer 40's which had a tendency for the wing to fail if this was not done.
I haven't seen the structure of this P-51, but many larger models allow the wings to come apart for easier storage and transport and have no issues.
I don't know many people that would want a 96 inch span model that you couldn't separate the wing into 2 (or more) panels for transport.
When in doubt, if transport is not a problem, I glue and fiberglass the joint.