Trying to identify. Not much to go on.

[komputatek]

Thanks for all the help. I've just measured the round front of the receiver and it's 1.295. someone else has said their Spanish Mauser was this dimension. Were the Spanish Void of any crest or markings on the front top of the receiver?

I also watched the video attached by UNPRO. Should I use a bolt with the gas port in it like the one in the video?

Information

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[vintage hunter]

Were the Spanish Void of any crest or markings on the front top of the receiver?

I'm pretty sure they all had crests when new but some may have lost them during rebuild. These rifles had long hard service lives and may have been subjected to multiple overhauls. This also may have something to do with the varying receiver ring dimensions.
Yes I would definitely use a bolt with a gas escape port. This is a safety feature to vent the gasses in the event of a case separation and hopefully prevent a catastrophic failure. If your planning on using this receiver for a custom build stick with a cartridge that has a max working pressure of 47,000 psi or less. Preferably less. The heat treatment and metallurgy of the Spanish made receivers is questionable at best.