It would help to get the whole VIN for your car and full type number for the current engine.

There were produced some 52 700 cars of the 1968 Volvo 144, from serial number 37 100 to 89 799. The last 6 digits of the VIN is the serial number of the car.

There were maybe 200+ different B18/B20 engines made. All have a 6 digit typecode, some digits in the cast and the rest stamped.

140 series used 77 variations of the B18/B20 engine. All started with 49. All B18 had 4968xx and all B20 had 4969xx/ 4980xx/ 4982xx.

A B18B engine in a 1968 144S, with M40, US version, should have a type code either 496836 (without exhaust cleaning) or 496865 (with exhaust cleaning).

Your current engine, with I guess typenumber 498191, is not from a 140. Its a B20F engine, most likely from a 1972-1973 P1800E/ES.