That makes some sense regarding the Intruder gears matching the 440 Invader. If the Invader achieved 88 mph at 8000 RPM with those gears, the Intruder, with it's power peak at 7000 RPM, would achieve 77 mph with those same gears...sounds reasonable. Surprised the HP was really that high from an Intruder.
I was almost sure the 340 Invader was under 56 HP. Back in the late 70's the cross country racing circuit at the time had a 56 HP limit. I distinctly remember John Deere had a "cross-country" kit available for their 440 Liquifire. It was a de-tune kit, designed to drop the 440 down to the 56 HP limit...if I remember correctly, it included different cylinders, heads, and clutch parts to work with the new de-tuned motor. JD didn't have any 340 Liquifires from 1980 and up...maybe a couple prototypes....so they had to de-tune their 440.
I thought the 340 Invader was good to go for that 56 HP rule. Jay Sperry certainly didn't do too badly with one in either the 77-78 season or the next year. I think he finished 2nd in total points, kinda a lone wolf effort against scads of Polaris TXLs, and others...
Yamaha's first SRV came out mid season as an 80 1/2 model, and they participated with it for 2 or 3 years on the CC circuit because it came stock with 56 HP. About 1983 ?? the rules must have changed, because Yamaha upped the HP to about 60 for the SRV motor.
Then Kawi, Deere, Scorpion, Arctic Cat bailed or went bankrupt...and the darned TXL Indy's ruled the CC races