The 2.1 cylinder head is much more robust, or at least better cooled than the 1.9, in fact I have never heard of one that has cracked yet, so if its flat it should be OK, you sound as though you know what you are doing.
I used ordinary bathroom sealer for mine and it doesn't leak, probably not what the purist would use! Because the engine was still in the car it was almost impossible to get the cam carrier between the head and inlet manifold without scraping the sealant, which was why I let it set, but you wont have that problem.
I wish you all the best, it should be a fairly straightforward job.
Is This Terminal? Part 4 – Some Answers at Last
Moderator: RichardW