A direct drive 49cc 4-stroke is not going to get over hills unless you gear it so low that ~20 mph would be your top speed on flat ground.
Like a 50T rear sprocket.
Middle of the road 'junk' transfer case, but the HS 142F is a top notch engine.
It's an HS 142F-engine the long shaft no clutch version.
That present problems for putting a transfer case on it.
The 5G un-adjustable dual chain transfer case is a mess.
It works dandy (though noisy) for say a few hundred miles and the chains and sprockets wear in.
After that no way to adjust it and 2 thin chains are not friendly to replace.
It is another cheap engine shaft mount clutch bell & sprocket system like the stage III or7G, so not ideal.
An original 4G or new 10G KCK will suite you better.
The clutch bell and sprocket are on a seprate bearing suppoted shaft and driven with a T-belt you can adjust.
I also think you are really better off with gearing.
You'll still bog up hills ~18 in first but you won't have to pedal, and on flat ground you can cruise at ~30+.
Not cheap, but if you want simple and reliable to get you around that's the ticket.