the most effective thing with stock parts beyond verifying everything is working as it should ( boost at 12psi, alda adjusted right, fuel filters, valve job, timing, ect, ect) would be to advance the timing slightly to around 26* adjust or remove the alda to prevent fuel limiting and finally adjust the governor in the pump. the max speed governor is easy to get to once you get the cover off. that will limit it pulling fuel till later in the rpm. i can say from experience that while the stock VE falls off a cliff after 4K with a bit of port work they pull hard to 6000 RPM.

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1985 300D om617: 8mm M pump 175cc 5200rpm, holset he221w @ 30psi, large A2W ic, compounds on the way.
KD9AFT
A&P