Whichever way you go please let us see what you end up with.
IDK for sure, but I think the Weaver Grand Slam bases like you have there are totally OOP, I have a suspicion that they are in fact Redfield bases, and either Weaver took over production of them for a while, or even just sold them off under their own name after Redfield stopped making them. Either way, they used to be very common and are now rare so you should be able to get back whatever money you have in it.
@Klenchblaize and
@Smellydog do raise a good point though, the ability to perform gross windage adjustments with the mount is not to be sniffed at, indeed, I have a Remington 788 I have "run out" of windage with and may look for such a base for it. Or maybe I will just put the Williams peep sight back on it and not bother with the scope.....
As to the OP, I have bases and rings that would almost certainly work for you but getting them to you from the USA is not likely to be cheaper than the Sportsmatch mounts you can buy directly, plus you get to support a British shooting company that actually makes a good quality consumer level product in the UK...