yes the G13B SOHC is the common replacement for the 100CC ,if you cant afford the G16A 16valve.Dont worry about fellas and installing SR20'S
Here are preferable engine choices for the Samurai,Jimny,Sierra
Suzuki G13B DOHC,G13B SOHC,G16A SOHC
VW 1.6 turbo diesel
Mazda 13B Rotary
All of these engines use the stock transmission with the help of an adapter plate and 4WD can be used.For high torque applications you will need HD transfer case mounts,engine mounts,beefier axles and t-case gears.Also these engines can easily be modified with the correct aftermarket part.
By the way there's a Suzuki thread for all Suzuki stuff