Below scale buses and lorries in many cases, due to space limitations, won't work on a typical 7mm layout.
(What annoyed me intensely, whilst searching for that elusive 1/43rd scale bus were the idiot sellers on ebay adertising Dinky, Corgi etc 1/50th buses and trucks as 1/43rd scale. )
I acquired a minichamps Mercedes O 3500 bus as a stand in, - the only real problem is its LHD and I now have german tourists on my early 1950's layout .
It looks vaguely like a Bedford OB, with a lot of fancy chrome bits and captures the period quite well. The minichamps detailing however is excellent, and in my view worth the cost...
(Minichamps also make some neat German (mainly Opel Blitz and Mercedes) trucks in 1/43rd)