The main pump is nestled in behind the magneto cover.  A smaller boost pump can be seen on the RHS - this makes up the internal leakage that all piston pumps experience.  The main pump is a bent-axis type, these are an engineering marvel in their own right- probably the most intricate piece of mechanical design in any field outside scientific instruments. Here is a link to a website with a reasonable description of how they work and some pictures but I'll try to explain it better.

  The pump consists of a number of pistons (9 in the case of the Dryvtech) radially arranged parallel to the pumps rotational axis (like the bullets in an old '6-shooter' handgun).  The pump is divided into two 'sections'; the 'piston block' containing the bores and the 'thrust plate assembly' to which the pistons and connecting rods are attached (via ball joints) and these two sections are connected via a universal joint and rotate together.  With the thrust plate's axis in line with the piston block's, the whole pump (piston block thrust plate and pistons) rotates around the pumps axis.  In this configuration the pistons do not move in the bores and the pump produces zero flow.  When the thrust plate assembly is moved 'off axis' (hence the name 'bent axis'), one side of the thrust plate becomes closer to the piston block than the other which produces a stroking action of the piston as it revolves around the pump's axis (which is now 'bent').  The angle at which the thrust plate assembly is offset relative to the piston block determines the stroke of the pistons and hence the flowrate of the pump.  In this way a continuously and infinitely variable flowrate is available which effectively gives the Dryvtech an infinitely variable gearbox.

Piston style hydraulic pumps and motors are made to an extremely high standard of precision- the pistons have no seals at all and run metal-to-metal, with an operating pressure of 4500psi (32 MPa) you can imagine how fine the tolerances must be.  These pumps are extremely expensive even compared to the normal prices associated with hydraulics. I bought the 2x2x2's pump from an aircraft wrecker who had it underneath a bench covered in filth.  Luckily all the plugs were in place and I parted with $40 for it in 1984 (I was still at university and $40 was a lot of money!).  My luck continued as I got a friend in the Airforce to check the serial numbers and it turned out to be brand new- only ever used as a spare part- out of a Sabre jet fighter in which it was used for the landing gear and air brakes.  I was working part time for a Vickers agent and, low and behold- spares were still available. I priced a reconditioning kit for it just out of interest- $18,500!  The drive shaft is a 30 mm long titanium number and a bargain at $3,200 (1984 prices)!