Well this could have been a disaster but it all turned out OK. I found an unopened pack of foil trays.
"Phew," (wiping my brow with the back of my hand.) "that was close!!!"
I began this by first analysing the original recipe for the slow cooked lamb and deciding on suitable "currified" ingredient substitutions. Possibly not surprisingly, once the Napolitano sauce was modified it turned out pretty similar to a base gravy and examination of JB's looked pretty close anyway so I made a reduced quantity of that first up.
For the pre-oven work on the main dish I cut the lamb smaller and only used 1/2 the quantity, then fried off some usual whole spices followed by onion and G/G paste then added the lamb to brown it off. I subbed in some red and green capsicum and green chilli for the carrots and celery before assembling the whole thing in a lidded cast iron Dutch oven.
5 hours in at 130'C and with a stir 1/2 way through and the result was a very pleasing, fall-apart lamb curry. (Slow Lamb). This shows a lot of potential for tweaking into any number of differently spiced dishes.