Different head sizes

[Targarich]

Hi

I am looking for help to understand why these two heads are different sizes for the same part number.

I needed to buy a single head because 1 of my original heads was cracked at the heat exchanger boss.

The height between the inlet and exhaust bosses are the same but the fins are larger on the replacement part.

Is there any reason, why I can't rebuild my engine with this part ?

https://flic.kr/p/vUSBj5

Thanks for you help

targarich