"Pardon my ignorance, but isn't a No4 mk1 an SMLE. I assumed it was as that is where it is listed on the e-gunparts website."
No worries there, indeed Numrich's web site misguided you. Typically, SMLE refers to the pre-No4 Lee Enfields (the No1 Mk3* being the most comon SMLE).
If you order the flash hider from Numrich, add $25 for processing the order shipped to Canada. Plus shipping, plus customs duty taxes once the package is in Canada, plus the fact that you've got 80 US cents for your dollar... So, by the time you get the flash hider, it'll easily cost $100.
So, you'd take a rifle that, short of the proper stock, is still an original ww2 firearm. It can easily be returned to its original configuration. On the other hand, you can cut the barrel, get something that could be less accurate (it would require proper recrowning at the very least), would be tougher to sell...
I would personnaly wait to find one that already had its barrel shortented... they are out there, and cheap...
Meanwhile, your still-intact No4 could eventually look like what it was once before. Here's one of mine, started sporterized just like yours; ended up like this after some work:
http://i272.photobucket.com/albums/jj180/louthepou/HPIM1206b.jpg