At only 5psi, despite no IC as long as you have proper control over timing and fuel, then pump fuel should not pose a problem. You could maybe even squeeze 10psi in

You could also use water injection if detonation cant be avoided..

But for such relatively small gains, it's hard to see how a twin turbo install would be worth the effort. Spend the money on the stroker, better heads, cam etc. You should easily see an extra 100bhp with that.

Other than perhaps the availability of cheap smallish turbos, I wouldnt even consider a twin install again. A bigger single would be much easier in every way. Well, unless I was buying an already fabricated kit. Twins are pretty much double the work.