When you wrote that it was a 399 I though it was the Free/air.
Coz I have a moto-ski grand-prix 1974 TS-400 and its a 399 Free-Air, same motor as the TNT 400 Free/air of 1974.
90Mph in 1974....Free-Air were real race motors
But Im always interessed by some picture
Moto-Ski Grand-Prix TS-400 F/A 1974
Moto-Ski Futura 500E 1981
F7 04 Fighter Pilot
Nissan Black 180sx 93, 340hp, the center car on my avatar