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. Twin Cam blocks came from 6 basic casting versions. Prior to 1968 the first 4 digits were often ground off the block and "3020" was stamped in its place.