You have mentioned a better option, that being the BOA/BOB V6, which is 200 HP/210HP respectively!

Yours is not a 4i engine, it's a late XR 4x4 engine, basically an enlarged 2.8 Cologne, they were 'claimed' as 150 HP, where as the 2.9 is supposted to make circa 160 HP IIRC, but they are not really that tunable.

The Cosworth V6 was from a Granada but it is a very popular conversion and I don't think it's a lot of work, seen as both share the same platform anyway.

Martin