Good Morning Trevor,
Congratulations that looks like a fine original car! It is known to the club and has been since at least 1991 when the owner joined the Club stating that his Father had bought it new on 3rd December 1948.
L997 is an early Saloon, the post war series started with L800 and is fitted with the Moss rear axle. Later cars had the ENV axle hence later cars have an EL chassis number. It also retains the early form of Lucas side light (L461 I think) rather that the later L488 type. It came out of the factory in National Grey livery, a colour which covers a multitude of shades, with beige upholstery and was supplied to Alfred Chaston Ltd for the first owner J.E. Jones of Pontllanfraith.
The illustration shows the position of the dipstick and is from the Manual, the club have reprints for sale. As Gary says the oil filter is on the exhaust side under the dynamo. I doubt if a Fram filter would have been fitted to your car, unless as a after market addition, as they were only fitted from 1951 ish. My Saloon did not have one (1950) but my brothers (1951) did!
I hope you enjoy the car,
Tom