I'd invest in better injectors, like SDX 5x.012's. Personally, I'd just grind the fuel plate to a 100 and start with it centered in the slots so you have a little room to slide it forward and back according to the happy median between your butt-dyno and EGT's. No need for the light spring, really...just snag the awesome AFC tuning writeup sticky and tune your AFC accordingly (the AFC doesn't add horsepower, it just helps control the smoke and the takeoff grunt really...). Also, being a current PhatShaft 62 runner, I'd suggest upping the ante for a Silver Bullet unless you can handle a little turbo lag...I know that mine leaves a little bit to be desired.
All that in mind, plus a little timing bump and most likely a lift pump upgrade, you'll probably be in the running for right around 400 hp if everything is tuned correctly and the engine is tight. If not, perhaps look into the article that Diesel Power Magazine just ran on a "400 hp kit" for the P-pump Cummins that involves a HX35 exhaust housing upgrade, injectors, modified delivery valve springs, rack plug and some other hocus pocus all in a $1500 kit, iirc.
Might be worth a look...
Good luck on the Fummins build! Glad to see another OBS Ford getting Cummins power!