Nitrous is classed as forced induction in race classes as far as I'm aware. I've ran it myself and once in an ly7 but that was dodgy af.
With the mods you've got an manual I'd assume without the nitrous on a stock manifold you're looking at 210-230 rwhp tuned.
I'd be using a wet injection with a trigger box that pulls timing when the system is armed.
A 75 shot should get you close to 300 rwhp. I can't talk for drive train loss on these or most because I don't use engine dyno's. I've always used chassis dyno's.
But with an OTR , full exhaust , manifold spacers , tune and some giggle I'd be confident the rwhp would be in the 3's.