a T5/T7 head would be the better way to go. no need to port it, just modify it to fit the T16 in your C900 (its not a bolt on.. which is the only downside)
from memory the front of the head needs to be extended to match the timing cover, i have seen it done on here somewhere, a plate is welded onto the head and faced.
There are lots of ways to fit the T7 head. Essentially there is a gap to cover up. Without covering the gap the engine oil will escape. So pretty simple to sort this out one way or another. There have been some very elaborate solutions over the years.