With a little checking, it seems that Drysdale happily used British components. A guide to what was available in the period is found in this extract from the 1957 Holdsworth 'Aids. Please note that Holdsworth promoted his own 'in-house' components first.
Then I would encourage you to look at the Readers Bikes on Classic Lightweights to see what Readers have used on their bikes for the timeframe of your project. The GB Hiduminium Spearpoint stem came in a variety of lengths and are often seen for sale (because they were widely used!) The same goes for GB Maes handlebars.