There is no manifold adaptor!:bang:
What has been done, traditionally, is to make up a plate to fit to the T15 (from, say, 8 or 10mm mild steel) and weld it onto a cut down manifold. This isn't a particularly easy welding job as you're joining two dissimilar metals.
Nor is it the best way to do it
And the different expansion rates must lead to cracking over time