I haven't used a Caravan block, but yes... they're "almost" the same. I don't know what is meant by "changing the oil passage" unless it's referring to moving the oil filter adapter to the opposite side of the block. I'd stay away from that block.

If you want a better block, use one from a SOHC Diamante... '92-'95, I think. That block has an extra strong webbing cast into the skirt and should be much stiffer than the Montero block. You have to grind off 2 locating pins, but everything else is ready to go. The pistons and cams are different, but you can use the Montero heads/cams, swap cams or use the Diamante heads/cams - your choice. The Diamante cams should give a little better mid-upper range power. The pistons would be replaced with any rebuild, anyway, so use the Montero pistons to keep the static compression ratio to the stock 8.9:1.

If you swap to any other block, make sure you keep your old engine for any needed parts to do the swap.

Frank