hay i have a xe falcon spac i have rebuilt the engine 5000 ago new every thing and still have about twenty oil pressure it has been worked would this be a reason for sum low oil pressure new pump and all has been put in

Try writing so we can read it easy..

No matter what mods the crank and internal parts require oil pressure..
I suggest changing oil sender unit ... Or double check with temp mech oil pressure guage..
Unless cam has been ground way wrong or excess bearing clearance oil pressure should be fine with correct clearance, assembly...