Pre-War Winchester Model 70 Super Grade question

[TxMike]

I recently purchased a rifle that I can't seem to find any information about except the manufacture date. The rifle was built in 1940 has a Model 54 action but a Model 70 barrel, stock, bolt sweep, floorplate, etc. As far as I know, Winchester quit making model 54's in 1936 after an 11 year run. So why after 3 or 4 years use a 54 action to produce a "hybrid" model 70? Winchester list the serial number as good for a 54 action in 1940 so I assume that the rifle is genuine Winchester manufacture and not some gunsmith's idea of a joke.Any information on this or the name or web address of sources would be greatly appreciated.