Well it seems I might have mucked that up.

Some sources say we have a 3.5 BAR FPR, not 4 bar.

GM service manual is inconclusive as it gives a range of 51-59 PSI.

Try it out, see how it runs, if it runs lean, then you might need to lower those values to reflect this mistake.

I guess the real mistake is not finding out your true fuel pressure without vacuum on the FPR.