In 1976/77 the Yorkshire pairing of Elliot & Dungworth built three 'new' Pilbeams which they gave the nomenclature MP22. These three cars were 'copies' of the Pilbeam R22 which was itself a development of the R15.
Now R15 started life as a Brabham BT38 (chassis 28 to be precise).
The three MP22 chassis were all based on Brabham's. The question is which?
