Is there anyone who could help me to figure out if the engine is a 401 or 425? The car is a Buick Electra convertible 1965 but I dont know if its the original engine or if has been swapped earlier. As you can see at the pict the code at front passenger side is ending with 529 and there is a W before but there is something between and even before the W.. The casting number ends on 704= 425? I thought I read somewhere that convertibles only hade 401, wrong? Thanks in advance!