 The original cam along with the DOHC cam sprockets were driven by a long front-mounted, single-row ⅜-inch Reynolds roller timing chain.Early Lotus blocks were simply standard Ford production line items selected for having the thickest cylinder walls, and were identified by an "A" stamped into the timing cover mating face.Later blocks were specially cast with Twin Cam production in mind and identified by an "L" cast into the block under the engine mount.