The early 510 sender is identical except maybe for the retaining collar which is metric on the 510. Early roadster and RL411 engines have an SAE threaded collar, just save it and toss the metric 510 collar. Later Metric 5 main bearing 1600 type R engines [SN 40001 and on] are metric, so try the 510 collar against the one you removed, it's probably metric. To remove the old sender I had to snake a thin steel rod through the radiator cap to the base of the sender and drive it out [after removing the collar] with gentle and not so gentle tape of a small sledge hammer. It can be done, don't get pissed and crack your engines head!