I believe that 53 was the last year for the two acorn nut valve cover. You can easily put the old style two nut cover on any year 235 or 261 with the addition of two long rocker arm hold down bolts. Maybe someone did that on that 54 corvette. You can check for the four threaded holes on the head where the original four hole cover would have been bolted to originally.
The Corvette had a unique cover not used on other Chevrolet engines. The front tapers down a bit to allow for clearance due to the lower hood hight. IIRC (I'll have to check my Corvette references), the '54 Corvette engine is identical to the '53, with the only change being the air filter housings.
