Looks to me like that Presto concept has the potential to be more fun than any ponycar.
And these days the off road guys have driveshaft solutions like these:
Tom Wood's Custom Drive Shafts - Tom Woods Custom Drive Shafts Custom Driveshafts Specialist
Click on the top right option. That would allow you to extend the wheelbase by nearly 2 feet without touching the driveshaft.
But putting an engine in front of a centered driver means the driver would have to sit above a driveshaft, or 2 extra gearboxes to offset the shaft, neither of which is good.
So yes, the second seat will be a spacer. I was thinking of letting it be long enough for comfort on road trips. Drink holder, AM / FM / CD with speakers, which the front won't have, maybe even a laptop.
I'm 3D modeling it in SketchUp Make 2014, but I have no clue how to share it beyond a digital camera pic of what's on my PC screen. I'm using the free version, and I can only e-share those files with others who have the 2014 version. And I'm not even set up for a printer, which I don't have anyway.
Mopar has a good auto transaxle, except it is 100% computer controlled, and it is an automatic. But the gearing is pretty good, it is common in the cheap salvage yards, and it can hold decent power.