High oil pressure on Lotus

[25v6turbo]

My dad owns a 1974 Lotus Elite,which he has had for years...

He has recently done a top end rebuild,and it started today and ran well,but has a high oil pressure at 2000RPM on choke it was showing 80psi,it should be 40 psi at 3500,and drops to 5-10psi on idle,he used 15/40 grade oil(good quality)but didn,t leave it running for long through fear of popping an oil seal,what causes this and should he be alarmed???

Should he go down to 10/40 oil?

[Pete-M]

Pressure relief valve stuck, incorrect head gasket, incorrect oil filter or a blockage somewhere.

[Albert Ross]

Head gasket upside down, blocking the head oil feed?? Try to find out quickly, before it fucks the lot up.

[shite_meister]

What kind of guage is it? electrical or capillary? has that been ruled out?

[25v6turbo]

Update is all seems well,it dropped to 10psi on idle and rose to 30-40psi on higher revs,thanks for the ideas i put them all to my dad.