the .509 would be very close to the last choice I would use , the 6 pack is difficult to make work well with very low vacuum & the 509 make very low vacuum , I would lean towards an Engle K58 or a Lunati Voodoo grind he will be far happier ijn the long run , what is the rest of the combo ,. gears intake converter stall , what is he using the car for primarily , what RPM power band does he need ? I might change my cam choice based on these