Old 540 brushed motors

[covertfox]

Sorting through my vintage kit got me wondering what are folk running electric wise in the old chassis these days. Are there specific rules about it and does anyone still run brushed 540 motors? We used to like to have a good selection to cater for varying tracks and condition, also 2wd and 4wd so there's everything here from a standard 27 single to 13 doubles from memory. New spare brushes/springs and various armatures too. Any info gratefully received, cheers.