Yes, the blocks are the same. Everything else is different, all the innards, camshaft, head etc. Unless it's 5brg, then petrol and diesel cranks are the same. Both forged, and not cast. 3brg petrol cranks are cast, 3brg diesel cranks are forged.
It's why as a petrol it's pretty much indestructible. That being said, I've seen it done.I don't know enough about those old 2.25 engines, but you saying that is quite possible, I'm pretty certain/positive the old 6 pot Bedford engines the 300 petrol and the 330 diesel had the same block and was just a question of swapping all the relevant bits, so there probably no reason why that wasn't the case