kevin303: No, that is not an impossible dream, it is actually a pretty creative concept and when done right, quite a beautiful application.
There is much you can do with the SMLE action. As you know, one firm out there is building 45-70 rifles on the #4, Mk1 action - Gibbs it is. Now, before Gibbs did that, a fellow in England build a 45-90 on a 303 British action. It can be done, especially with the lower pressure rounds such as the lever action rounds. In that regard, the 45-70, 45-90, 444 Marlin, and some of the 35 caliber lever actions come to mind. And, you have mentioned some of the European cartridges too, so there are lots of options.
Believe me, a nicely customized #4, Mk1 in 45-70 or 444 Marlin would be a prized member of my collection, and one that got significant use.
Go for it friend, and I hope to read about your success and see some of your efforts posted for the world to appreciate. Mikey.