There are all sorts of mustang II-based front ends out there, such as Heidt's or Fatman, and they have been working for years. I believe with most of those setups you keep your existing framerails. The aftermarket is full of upgrade parts for this basic setup. The same basic setup was used on the Granada so don't let someone tell you it isn't strong enough.
The Dakota swap is very popular here and it looks like that's because it is a good one. People either swap the whole frame or else cut and weld the new front end to the old back half of the frame.
I wonder when Dakotas are going to become scarce, they aren't really valued for much else and they are scarce on the roads right now. Probably quite a few sitting besides barns, though.
R.
I know you aren't going the Mustang II route, but FYI, the Granada doesn't use the Mustang II design front suspension, but rather is a modified version of the high mount coil design originally developed for the 1960 Falcon and later used in the original 1965-1973 Mustang and 1962-1971 Fairlanes and Torinos.
The Mustang II suspension was used in the subcompact Pinto and 1974-78 Mustang and Mercury equivalents
