I was out of pickle spice and Kroger did not have it. So I looked up a few recipes and averaged them with the spices I had on hand. I used ground ginger and apparently that made the solution cloudy, I have a Bay tree so it is pretty heavy on the bay. I used prepared mustard as I had no seed. But how much flavor difference can there be when it is done and I then simmer it with garlic, etc . It may be a little different as I am making the corned beef from a pork loin.
The exact spice blend for any 'Pickling Spice' varies from maker to maker, from region to region, from season to season, etc...
It sounds like you found substitutes for each of the basic flavor components, so this plan looks good so far. The 'corning' process traditionally is a long, slow process which is usually approximated by a spice blend that gives a similar flavor, and a long, slow cooking process that cooks but leaves the meat tender. There is more about the history, and how 'Corned Beef' is not a traditional Irish dish in this article.
Your use of pork loin is another substitution, and be careful, as the loin is relatively more lean that the brisket that corned beef is usually prepared with. Check on cooking time, as a several hour simmer, which is great for a 3# brisket, could make the pork very dry.
The cloudiness from the ginger will resolve as all the spices simmer together, and protein will come out of the meat. You aere on the right track, just know that you are making an interpretation of the dish, as a number of variables have changed. Cook, enjoy, take notes, adjust.
Powdered or dried spices have a different flavor than fresh. Not always worse or one-noted but usually that is the case. So will it taste different than if you used fresh? Absolutely.
But being that your planning on using a pre-made pickling spice either way, as long as your included the same spices it should taste the same.