Hello, I will keep this one simple and short (if possible):
Yes a 5 speed conversion has been developed for the Viva using a Type 9 ford gearbox by a very helpful man on this forum with a user-name of "House".
Basically one needs to cut up your existing gearbox in order to make a bell housing that can be bolted to a type 9, a modification is also required to the flywheel so it can fit a Ford Sierra clutch plate and a custom clutch arm. You would also need a new prop-shaft and crossbeam to support the gearbox. House I think can do most of this work for you (at a cost).
Now on the HB / HC and Chevette this is a straight forward fit, BUT not on the HA as it has a much smaller prop-shaft tunnel, which implies the gearbox will not fit in the tunnel as its larger than the original gearbox. One MAY have to cut the gearbox tunnel and this creates a whole series of issues in itself. I have one of these gearboxes all set aside for my HA but have yet to find the time to fit it and confirm my fears.
Why not speak to "House" and find out some details ....