M50B20 vs M50B25 head

[Slowcar]

Hi Everyone,Are there stamping marks on the outside of the cylinder heads to positively indentify a M50B20 head from a M50B25 head? M50B25 heads are hard to find in Singapore and I am worried that a sneaky mechanic may replace a cracked M50B25 head with a M50B20 head.Do you know if the heads are interchangeable? Just bought a 525 and although the low end is much better than old 520, the high end seems flat.Peter.