True you are in the UK and any head will be "overseas". I guess the real question is do you want to spend money on a gamble you'll get a useable part from Speedmaster (my personal experience is that's a poor bet), and even though everything for you is overseas would you prefer to spend your money with a country that hates you, or one that is friendly?
There are better options available. Since everything will have to be freighted to you, there are lots of good used Edelbrocks or similar if you aren't in a hurry.
Although I try to avoid chinese stuff when possible, it isn't always. At least outfits like Scat are ding their own quality control and machining. Speedmaster is just terrible in every respect.
I do have to give credit to Summit for fixing the issue. Not that they aren't without flaws, but Summit is at least still a privately held company that does a pretty good job in the modern world of keeping their business here compared to selling to some investment company.