I've several Chiefs. Also have ridden your proposed route. Rather than toss $1,000 away on bigger tanks I'd take a couple of cheap plastic 2 & 1/2 gallon tanks and strap them on the top of your saddle bags/boxes, then give 'em away as you get closer to "civilization." Ride 70 miles, fill up your tank(s) (rest your hands from the vibration) and start looking for gas. Gas was plentiful as noted in the previous post. After you squirt yourself and your bike a couple of times you'll get the knack of telling the old girl in the gas station cage exactly how much you need.
It's the bag of spare parts, tubes, nuts and bolts I'd spend $ on. Mike at KIWI has what you need when you break down, but getting it there within a week to 10 days will be tough for DHL, Fed Ex, etc. Might make sense to just buy a used Japanese car in Japan, ship it across for some guy to follow you carrying the spares, then sell it in Moscow. Heck, add a camera, physician, mechanic, "fixer", camera guy, and bingo, You can call your ride the Indian Star Wars Adventure, cry when you reach Moscow and get someone to write your book/peddle the DVD and you're famous.
Seriously, about 1966 I met a guy who was doing Europe on his '48. Nuts/bolts were his major problem (everything was metric). He ended up using Volkswagon tires when he needed new rubber, and had the mag rewound when it died. He paid the extra $ to get rid of the distributor, that way was not dependant on the crap Indian relay/generator. In the end he said his ride was more of a torture test than fun. I'm sure you've made contact with Lenord who flogged his Chief 2-3 times in the Iron Butt Ride. If not, it'd be worth the time. I don't think he ever got more than 2/3rds of the way through, but could tell you were the weak links in his chain were over the long day-to-day ride. I love my Chiefs, and to ride one, even across town, is always an adventure - not knowing if it has to come back home in the back of a truck. The good news for you: There's lot's of trucks on your route.
All the best
Gregory W. Frazier

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Sun Chaser, or 'Dr.G', Professor of Motorcycle Adventure at SOUND RIDER magazine. Professional Motorcycle Adventurer/Indian Motorcycle Racer/journalist/author/global economist/World's # 1 Motorcycle Adventure Sleeper & Wastrel
Soul Sensual Survivor: www.greataroundtheworldmotorcycleadventurerally.co m