Is it the same as the 6 cylinder out of rover cars (possibly the p4?), if it is it might be worth asking on a rover forum, sure theres more of them than 6 pot series
A lot of 2.6 blocks have been scrapped due to poor MPG, so there must be some good second hand spares out there.
Unfortunately, the outlet to the exhaust is in a different location vs the P4 due to other bits in the way. So, the parts aren't interchangeable.