The ride along Rio sounds awesome and really jealous!
That board looks like it’s got some miles! A quick re-grip and i’m sure it’s ready for a lot more. I would keep an eye around the mounts as i see some cracks - also being a heavy guy make sure it’s not stressed and may fail on you at speed (that would suck).
If you are able to make your own mounts - this will be pretty straight forward for you.
Clearance for the motor mount likely will mean you need to move your trucks to bottom mount under the deck. Even if everything else clears the clamp portion of the mount usually sits right where it’s in the way. It’ll depend on your trucks for sure and not being there it may not, but i bet it will be tight or hit at lean.
I would suggest Aluminum vs Fiberglass for the motor mount portion of your mount. Aluminum will be stronger, and conduct heat from the motor (acts as heatsink) helping it cool a bit more. Enertion uses a carbonfiber mount on one of theirs, but it’s also pretty beefy (and doesn’t aid in cooling). I’m not sure GF/FG is up to the job strength-wise.
Especially the thin sections at the clamp/rotate side - those thin interior walls i would be very suspicious of and imagine they are an early failure point of GF.
Wheels - you’ll have to drill through the eurothane to mount your wheel gear. Being only 70mm they are a bit small so you will have less ground clearance under the belt/gear. You can run a lower tooth wheel gear to help clear - but this will also equal less torque/start-up speed and acceleration, and poor hill performance. Maybe not an issue on the flats in Rio - but the hills will be a problem - especially for a bigger guy.
The duro of those wheels at 80 is going to be hard - so a lot of bump/vibration will be transfered. Not a huge deal, but on long rides you may feel it and be tougher to ride for longer distances/time. Especially if riding on rougher roads. Bigger and softer always helps, but if you are trying to stay within a budget, or just use what you have vs ordering something new - i think it’ll work for the first try. You may upgrade later to get it to ride better, softer, etc.
If you have some fabrication skills and can work with epoxy (assuming so since you talk about making GF mount) - take a look at whitepony, okp, and others who recess the batteries into the bottom of the board. 18650 cells are only 19mm(ish - vary a bit) - so really can be a great option. But you’ll need to reinforce and protect them (like any battery really).
Look forward to pics of the project - and pics of your ride through Rio!
Best of luck!
Thanks for the replies. 
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