It would make sense to send the shell to needy friends in Karachi...
Buddy you need a 1.3, not higher than that and not lower than that, nice and manageable and very quick for that tiny 680kg body. Also I would recommend a simple set up, carby engine ideally, unless you get a Busa engine and kit which would just be the dogs bollocks consider something simpler and the torque and braking of which can be managed easily.
I have seen a d15b and lots of money spent on it yet the damn thing still never ran properly, the engine bay was so tight that you couldn't get a hand in there without opening 20 things up, and then the weight just threw the geometry out to the dogs. Eventually the guy just put a Suzuki M13 in there.
So to sum up:
1.3
Carby
Close weight to the A series 1275 i4
Live happily ever after
OR, Option 2:
Send to Karachi
Live happily ever after