First off, are you sure you want to be fitting a XE? For the money involved these days its starting to look like a dear option considering all the other possible engine&box combo's out there.......just my opinion tho
I havent done an XE into a Viva but i can give you a rough idea of whats involved from what ive learned from others.
Crossmember - Either will do as you will be modding the engine mounts anyway, but if poss use the bigger engined variety as you will need the bigger brakes.
Gearbox - Ideally would be a Manta Getrag 5-speed 'box as its tried&tested, but cost&availbilty might be an issue. If not then a Carlton gearbox will do the same job for less monies but is quite a bit bigger
.......failing that then a ford Type9 with a suitible bellhousing will do just nicely. Both the Manta & Carlton 'box's will need the tunnel opening out, but you should get away with not touching the tunnel if using the Type9
Prop - Depends on the gearbox used, but a hybrid isnt that hard to make or there are specialist companys who can build you one to your specs
Sump - Manta alloy big-wing sump is the tried&tested one to use, but same as the gearbox's they are going up in value and getting harder to find. Failing that there was a company making up steel sumps for RWD use....but cant remember the name
Diff(rear axle) - Magnum/Firenza 1800/2300 Axle can handle the power, with the correct arms its a straight bolt-in replacement for the smaller axles.
Hope some of this helps
Steve