Most early 911 up to 1973 use a specific T bolt to hold the front and rear bumper trim on. From Porsche these are £1.38 each and each car needs 20 (total £27.60).  Canford Classics thus made a batch and can offer these at 95 pence each (£19 for a complete set of 20).

95P  each (plus VAT if within the EU)