RC: The XR4Ti is not even a cousin of the Capri. That's a Ford based chassis. The Capri is a Mazda.
Custom mounts would really be the least of your worries. You're forgetting a drive tunnel in the floor, no room for a rear diff, etc, etc...
BlewItUp: I think there are a lot of domestically available options here that might be a better choice for an AWD donor - a whole DSM drivetrain would work really well & offer a very potent powerplant with lots of bolt-on parts availble. (yes, Jamie - I said DSM!)
Check out this guy's conversion:
http://www.performancecar.co.nz/articles/mazda/heart-of-diamonds-mazda-323-gtx-familia-125 Keep in mind though, he was already AWD. Personally I think this would be one of the most practical & realistic routes for a reliable AWD conversion you could really beat on
I have been quite fond of the idea of a Subaru drivetrain too, the low center of gravity on the Boxer motor & symmetrical AWD is very appealing, and so is the 300hp from the STi engine
The less potent RS engines seem to be more readily available though, and don't demand quite the premium an STi dropout does...
Here's a Honda with a Subaru powerplant & drivetrain:
http://honda-tech.com/showthread.php?t=2763036