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You should be able to swap-out the in-tank fuel pump to an EP386. I did the opposite back in the day with my Crew Cab swap to an LS. Here is some information that might help you? http://forum.73-87chevytrucks.com/smforum/index.php?topic=34789.msg295493#msg295493Alternatively, while not an inexpensive solution, Vaporworx can provide you with a PWM unit to reduce the speed and hence control the pressure in your fuel system. Check-out: https://www.vaporworx.com/shop/product/returnx-return-type-pwm-controller/
GM TBI needs 11-14lbs. The regulator in the TBI controls the pressure. The Walbro GSL395 is the same as what Holley sells I have no experience with the above listed. I would highly recommend moving to a submersible intank pump at some point. This will increase the life of the pump and will run MUCH quieter...
The Summit 03-0067 kit has a 14 psi rated fuel pump with a regulator. This would suffice, no?