If they have a glut of SR 8 planks and 6 wheel brake vans (and similar) the alternative would be to offer specific packs - those three in the £100 pack equate to £58.70, now I have seen the 8 planks on sale around £23.50 but even then getting the brake for £11.70 is a still a bit of bargain.
Do wonder how much unwanted is going to appear one ebay shortly.
An alternative approach would be to have a selection form where you could mark what you do not want in the mystery pack and dependning how many you tick off whether then you are only limited to the £100 one. If for example I could say no to any Lion, J70, 15xx or tramcar then I might be tempted.