first of all is this for your first car OR is this for your first classic car...because if it's for your first car i wouldn't reccomend any that you have mentioned...go for a mainstream car like the CRX first gen,honda beat(with a sensible owner),sprinter trueno...
i don't think you can get any triumph convertible or a sunbeam for under 500k....all triumph TR series cars go for more than that(maybe supra_natural could enlighten us about the spitfire) and the sunbeam roadsters(alpine mk1,mk iv,talbot) are very rare and expensive
the capri is an excellant car,,if you can find one in good nick;..don't know abt the price...i'll let the landy experts talk about the LR.
how about adding these cars to the list
*renault feugo
*mazda rx7 savanah
*mini
*mini moke
*morris minor tourer
*ford escort mk1