Yes, a Thriftmaster is a truck engine, passenger would be a Blue Flame. Also, up to about mid '56, solid lifter and hydraulic lifter engines used different blocks, so a serial number verification might be in order to determine what engine it really is.
But like Stuart says, if it's solid lifter, it's supposed to be noisy. Not exessively noisy, which would indicate a need for maintaince, namely a valve adjustment.
