Your Minor is a '58, so you shouldn't need Whitworth spanners or sockets (sorry, I can't call them wrenches, it just doesn't seem right with Whitworth!) for the great majority of nuts and bolts. British cars were almost all UN threads by that time, and UN sizes are the same as American Standard.
There are a few exceptions, electrical and carburation, in small sizes of BA and BSF (under 1/4" thread size). Even though I have sets of BA and BSF tools that I've had in some cases for 50 years or more since I was a teenager in England, I've also found that those small-size combination AS/Metric sets you find in hardware stores work very well, particularly the 6-point hex sockets.
Note also that, unless your Minor is non-standard, you won't need a Unisyn, which is good for synchronising twin carbs. You should have a single 1.25" SU.
With all the money you've saved by not buying stuff you don't need, you can afford to buy a new Gunson Colortune. Get the 14mm one, around $50 - $60 or so.
Have fun!