Some cars leave a paper trail; the Brabham BT43 left a name and a place in Brabham's list. What follows is what can be said with a source behind it. The shape is credited to Geoff Ferris.
Where it came from
The Brabham BT43 was the only Formula 5000 racing car built by Motor Racing Developments (MRD). Initiated by Ron Tauranac, designed by Geoff Ferris, and built by a team including Nick Goozee (monocoque) and Bob Paton (construction), it was one of the last cars produced by MRD before MRD was closed by the then new Brabham owner Bernie Ecclestone. Based on the Formula Two Brabham BT40 (which was also designed by Geoff Ferris) the BT43 featured a modified monocoque that incorporated the triangular cross section pioneered by the Brabham BT42 Formula One car which was designed by Gordon Murray. This distinctive pyramid shape not only kept the aerodynamic "stagnation point" low but also neatly allowed the incorporation of a "crushable structure" as required by the 1973 regulations which specified that all fuel tanks were to be protected by deformable structures.
Engine and gearbox were the then de facto F5000 standard combination of a Chevrolet 302 cubic inch engine in an unstressed mounting and a Hewland DG300 gearbox. The fitment of these into what was a relatively small Formula Two sized car presented some design challenges. Front suspension components were BT40 while rear suspension components were a combination of Formula One and BT40. Rolled out in October 1973 and photographed by renowned motoring photographer David Phipps; the BT43 was initially tested at Silverstone by John Watson. This initial testing revealed a distinct lack of front end downforce.
In context
Nearby in the Brabham catalogue sit the Brabham BT18 and the Brabham BT62.