I would like to try to build that bicycle-pickup or cargo bike and use the Tanaka on it.
The inframe I have in mind will be a replica of a 1912 Norton I have a photo of. I'll have to stretch the frame and figure how to place the engine. I spend free time now shopping eBay for old springer front forks, old fenders, carbide carriage lights, and all the eye candy necessary to build a vintage replica out of.
Lately the last thing I got a wild hair to do was build that pusher trailer that would look like a tear drop trailer with a tent canvas top over the wagon. I already have a motor for that build. Just gotta get over to the scrap yard to see what's available in 1" square tubing and 3/4" rod
stock. I'd use the bike in the pictures above with the trailer. (can't legally use it here in Ohio though) Still I've been working with the calculator that Fair posted to find ratios and mph/rpm forecast. Looks like a 11 tooth centrifugal clutch and a minimum 80 tooth (8") gear for the drive shaft. (but 100+ would be better) The sprockets on the end of the drive and the wheels will be a 1:1. So, I'll have to go junkin on the scrap yard and see if I can find some old offroad go cart I could find that on. But I like rattin thru junk yards.
Obviously, I do alot of research before I go to the shop and bench.
Ya know...."measure twice cut once".