Interesting spec, pretty old school by the sounds of it. (no offense intended by that!)
Is it a real ko4 turbo? as in a ko4-022/023? or a ko4-001?
if it's a ko4-001 then that's a decent and typical result, they can be taken further, but many will be around that figure.
if it's a proper ko4-022/023 then the result is really fairly low.