Brakes
The 8" brakes are not twin leading shoe, they are the same single leading shoe arrangement as the original brakes. I have Vincent Vleet's PVL twin leading shoe set up which fits in standard drums, and if the 8" brakes are half as good as those they'll still be a huge improvement over standard. They (PVL) give an immediate response, single finger application, and that is precisely what I couldn't get the single leading shoes to give. My 7" drums provided (and still provide) adequate stopping, not sensational, but adequate, but they were very slow to bite. I found this nerve-racking in traffic where if the guy in front stops, half your space is eaten by reaction time, and a slow response from the brakes on top of that...
The 4ls kit cost about £1000 when I bought it, but this was governed by the GBP/Euro rate, at that time favourable. It was complete, and fitted straight on in about an hour. They may however have been reduced in price since (from a casual remark I overheard) so you really need to ask PVL. If "all" you want are decent brakes, discs are undoubtedly the best and (by far) cheapest option. 8" brakes are £975 from VOC, plus, I think, cables and maybe a new hollow axle.
What is the cost of the 4SL set up? I like the sound of it.