DO NOT TRY AND FIT A FORD ENGINE INTO A VAUXHALL!!! The cost in getting a V6 Ford engine to fit will not be cheap but as mentioned above the Vauxhall V6 into a Corsa has been done a few times now and suprisingly isn't that hard to do. Plus you can still use the Corsa gearbox (even though it wont last aslong) Regal and Courtenay both do a conversion kit for this very engine (2.5 or 3.0, mounts are all the same) and isn't that expensive.
If doing the conversion on something as small as a Corsa, dont think about changing the rear drums to disks as will lock the back end up very easily at speed (happened to 2 of my mates) so instead uprate the front and change all hoses for braded

Next do the suspension and that will be easy to do. Custom made exhaust to match the new engine and jobs a good'n.
If thinking about the rear wheel drive version, then think along the lines of the Vauxhall Omega (try and get a whole car and you will have everything very cheap for the conversion). The V6 engine in this car is mountewd traversly to enable the drive shaft to run to the back. If you get hold of a whole Omega car, you could swap the whole system over to the Corsa with a bit of chop and weld

Shorten the rear drive shaft and bobs ya uncle.
I've helped convert 4 Corsas over the years so if in doubt, just ask for help mate