Other ways to tell the difference from a 340 to a 273 or 318 by not reading the side of the block. Motor mount ears are different on the driver side on the 340 then the others for one. Not a exact science but pull out a plug and check the heat rating. What tells me mostly it not being a 340 or any other "RACE" motor is the exhaust manifolds are not for racing. The intake looks like a old style Edelbrock Performer 4BBL intake, which has the angle thermostat housing. I first thought it may be a 64-65 273 stock 4BBL intake, but not sure, I can't dig mine out to check the angle of the thermostat housing. The part # starts with a 24 (don't have the full part # with me now) and if it does on the car it must be a 273 because it will not fit on the other small blocks. It is a COOL car to own and play with but I think someone in the way pass added parts to a 273 or 318 because the valves covers may of came from a late 60's SB as well as the water pump from the 60's. All said and done, the OP needs to climb under the car and check the casting #'s to be sure of the motor size and then remove the valve covers to check to head casting numbers also, so he knows for sure what he is dealing with.