From what I can read its possible a ZF'd gun was sent back to be FTR'd if it was repairable. Ive seen notes that the receivers were welded up and re-machined.

Where is it marked ZF?

What no is the bolt head?

Its also possible that you have a surplus part bought to refurb a gun that was then sold to you as Ive seen an Ishapor with a DP painted forestock that otherwise was fine.

If you have a gun and it looks good, I'd suggest finding a gunsmith who knows Enfields and pointing this out, get it checked.

It would also depend on what the gun was. If it was a T then its valuable as a piece of history and simply keep it as such.

Otherwise Enfields are pretty cheap in the US and there are some mint ones about....

regards