Bloody Mary's chassis was unusual in having three longitudinal members instead of the usual two. Here's what JVB wrote about it in his Profile Publication on the car:
The chassis was made from ash, and it is still free from woodworm. There are three fore-and-aft members, the central one passing between the driver and the power plant, and two cross-members, one at either end. They are joined together with steel angle brackets and bolts, all the holes, both in wood and metal, having been made with a hand-operated breast drill. It was a painful and laborious task.
Richard Bolster, JVB's brother, built his Bolster Special around a GN chassis.