How to flush out a new build

I had my race motor rebuilt. Apparently the machine shop the builder used did not boil the block. Now it loses oil pressure because the pickup screen keeps getting clogged with gunk. I backflushed the pickup tube and it restored normal oil pressure for a while, that's how I know. There are NO spun bearings! No metal shavings in the oil, just gunk.
Is there a way to clean out the oil passages without disassembling the motor?
Flushing crankcase with diesel?
Other suggestions? Taking it back to the builder is not an option.
:-(