Just to try and keep this thread informative, there are alternatives to the 1.6 gas swap and the td swap.
Carb Conversions.
these guys offer a kit to remove the stok carb and intake manifold old bolt up an adapter manifold to use a 44mm Harley-Davidson sidedraft carb. This gives increased performance, no stallin-on-an-angle problems, and increased fuel efficiency.
An alternative is something like
this, although it appears he is no longer selling them. (wouldn't be too difficult to fab myself).
One dyno-proven report stated a freshly rebuilt 1.3 at 40 hp at the wheels, with a header and weber carb was 55 hp, and with the 4 GSX carbs it was 76! That's almost
twice the power! This guy also states that, with proper and careful tuning, he saw
33 mpg in 50 mph country driving with a small lift and 31" tires. Needless to say, it's very impressive.
This may be a better alternative to a complete swap, depending on the condition of your 1.3, and how fab-savvy you (or your friends) are.