I think you're on the right path using the middle of the valve cycle for the injection point. Alternatively set the engine as half the number of cylinders and wire the injectors up as pairs. As mentioned, the MS3/3x does this, using the injector timing table timed to the middle of the valve event with a low duty cycle. The lower the HP production of the engine the cheaper it is to get injectors large enough to fit the duty cycle window. Its still a compromise, but it would be pretty close if the cam doesn't have a ton of overlap. I'd be curious to know what the high end of HP production is for Packard straight 8 is?
700HP, 25% duty cycle can use commonly found 2000cc injectors ($$$ though).
300HP, 25% duty cycle can get away with a much cheaper 750cc or 800cc injector.
https://www.witchhunter.com/injectorcalc1.php
