Oil pressure relief valve removal (1275)

[midget]

I am in the early stages of rebuilding a 1275 block of unknown heritage, but believe that it's a Marina.It has been standing unused for many years.
It is currently soaking in Citric acid and have just realised that the oil pressure relief valve is stuck fast in it's housing. I note that Phil suggested retrieving it by oil pressure, but obviously this is not possible at the moment.
Have studied the schematic picture showing the galleries route map, and wonder that if I blocked all the appropriate exit points around the section of the valve that it would be possible to eject with air pressure?
Any other method please?

[les]

If you’ve got a long tap of suitable size, screw it in lightly and see if it will move the plunger. If not maybe a long stud that will fit tight enough to grip.

[midget]

Ok Les, thanks but panic over!
I put a 3/8 drive socket extension into the valve and it was very close to fitting,so I wrapped a piece of emery around the end, and out it popped!