Motobecane 50V Restomod/EV conversion

Dan River /
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Hey gang, I've got what I believe (the VIN plate is quite faded) is a 1970 Motobecane 50V... well, really it's the Canadian N50 but as I understand they're basically the same. I bought it off a guy who wasn't the original owner. He had a plan to rebuild it a long time ago. He stripped some parts off, took the engine out and somehow lost it (how do you lose an engine?) and then it sat in storage for who knows how long. I found a lot of old vines around the drivetrain so I think he's using the term "storage" pretty loosely.

Its current state:

The frame and bodywork look to be in okay-ish condition with not too much rust. Not sure what state the inside of the gas tank is in, but I suspect it's not great. Front and rear fenders are both there and in decent condition. It's missing the chain guards, but It looks like replacements are easily found online.

The rear shocks are quite rusted (I'll try to salvage them with an electrolysis bath). The front and rear brakes will definitely need to be replaced. I'm hoping the front forks can be cleaned up and aren't too far gone.

The headlight is in decent shape, the shroud is a little rusted but can be brought back to life. The lower plastic grill is cracked, but I looked quickly online and I think that can be replaced. The taillight looks pristine. Probably the best part on the whole bike!

The speedometer bezel is extremely rusted and the numbers on the gauge have faded. I quickly shot some lube in the speedo cable and was able to move the needle with a drill so I might try to restore that if I'm feeling ambitious.

The plan:

I want to give this moped a second life and build it as a city commuter for my wife to go back and forth to work (about 20km round trip). That means it needs to...

1) Be extremely easy to operate.

2) Look great.

To accomplish the first point, I'm going to convert the bike to electric. So no two-stroke braapp unfortunately. I know, I know... please don't ban me from the forum for this.

To accomplish the second point, I'm going to preserve as much from the original as possible, simplifying the drivetrain and concealing the battery/electronics into the bike's design.

Ideally, I'd like to use a rear hub motor. This would eliminate the need for any chain or pully on the left side of the bike and free up space where the gas engine would mount. I do still need the freewheel connected to the pedals on the right side to make it legal, but that's easy enough.

The first issue I've got to solve is I need a dropout width of 150mm and the stock swingarm is 125mm. That seems a bit far to reasonably stretch and I would like to avoid chopping and welding a perfectly good swingarm that someone else could use.

Does anyone know if there's a wider swingarm that would work on the 50? Maybe something like this? https://www.treatland.tv/MLM-motobecane-MBK-51-style-race-swingarm-p/swingarm-894-and-pegs-893.htm

Oh, here's a few shots of the bike in it's current shape...

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