Jet ski motor not to good for a buggy. To hard to tap power off the crank where the inpeller drive used to be. The cransk have been know to break when conveted. Waters "slippage" allows them to survive.
The chevy Impala V6 might be a tad heavier than you like but if you made something like a Sandrockets machine you can get aways with a salvage yard rear IRS. (Is the Impala front wheel drive? I think it is. You can still build something like that around a front drive motor sideways with the diff locked and a driveshaft running back to the IRS diff)
Sand Rocket - The Ultimate V8 Sandrail - Featured Sandrockets
Using the cars front drive tranny bolted right to the motor makes them offest far to one side or really short travel on the short driveshaft side.
The Cobalt motor has potential. People make adatpers that bolt to thee crank and then a CVT (sled clutch) bolts to that. But then you need to fab a rear drivetrain or buy a RPM tranny or a Jeffco (2500 to 3500 respectively) to have reverse.
Do you want this thing to be automatic or manual shifting?
Lighter weight machines are gonan tend to be faster (all else the same) and nothing handles better than a light machine for the most part. (read nimble)
You "might" consider selling off the motors and what you have and buying a bike motor if you want shifting. If not a sled motor might be a ticket for you. The cobalt motor you have has EVERYTHING neede to make it run right now? A lot of people like those. Good HP and a lot of torque. Plus you can beef it up a lil IF you wish and your drivetrain can handle the power.
You said long travel. I have seen 15 inches alled long travel and some do not consider it long travel til they hit 20 plus.
Either one is gonna need some good 930 CV's or some "home brew" use of modern day front drive CV's that can take angle but have no plunge so other means of plunge have to be built.
What kind of suspension front and rear you looking at?
Just an old fart from Florence Oregon
(Jsut some food for thought) That link shows a neat way to use a common tranny for reverse and good gear reduction. Sprockets tend to limit ground cleanrance some VS a smaller gear.