Rare indeed! I have seen an ad for one for sale in Alberta - and partly own a parts car a few hours aways, and that may very well be it.
I truly don't know the differences - and, can't really seem to find out. However, it generally seems to have been a bit of a hodgepodge of SL and GT and ???
1. Yes, the centre insert in the grill for the Epic.
2. There do seem to have been Canadian Cars that had the hood with the scoops but a 1600 engine - I part stripped one (though the engine was gone - yet the owner assured me it had been a 1600)
3. The centre console is different here. Look at the picture in this thread:
viewtopic.php?f=2&t=20216 - and I have two exactly like it.
4. The LHD cars had a Vacuum servo for the brakes which I don't think they had in the UK
5. This is what the Viva Outlaws site says about Canadian cars: For the Canadian market it was known as the 'EPIC GT'. Basically this was half a Deluxe and half a Viva GT. The Deluxe parts being the trim and lack of bright work. Canada was one of the main importers of the Viva GT.
6. I have two different sets of front seats - the ones that came out of the parts GT look like what you would see in an SL.
So, to come back to the original question - other than the grill and the "epic" name badges, I am not sure.
Oh, and, if you read the Viva Outlaws site, all the cars that came to Canada were Envoy Epics, (which were sold at I think Chevrolet dealers) but somehow there were also Vauxhall Viva cars (sold in Pontiac dealers.)
But, coming back to the original question, beyond