oil pressure gauge???????

I bought a 20 bayou 1999 for my bo to replace a old suzuki 160. the previous owner replaced the cam a year ago, i assume due to no oil getting to valve train. I bought the bike and found that again no oil to top of head. i am replacing the cam and rockers and have cleaned the internial screen (what a stupid place for a screen) the bike runs good but would like to put a inline oil pressure gauge or light but i dont no what the pressure should be or if its even possable. any thoughts?