Sri-Lak,
Here's my 2 cents worth, Just get rid of the thing . It's not a classic, neither is it ever going to be. If it was in poor shape when you first got it and has Corolla bits on, it's going to be a costly nightmare for you to locate, purchase and ship stuff here. Then there's the question of putting it all together. At the end of the day you would have spent a shed load of money on an ordinary car.
The Cosworth is quite a specialized performance machine. It will be even a bigger task to convert it.
If you are crazy over a Sierra then that's fine, if not just sell it.