Here i will explain the things you need to do to the bottum end to get it raedy for the 16v head.
First thing i did was tap the oil returns in the front of the block and screwed in the new plugs. the block will be getting planed after all this.
then i blocked off the PCV hole and the oil feed holes.
(the red arrows are the oil return passages, the green arrow is the oil feed and the blue arrow is the PCV holes)
after that you can either drill holes in the back of the block or drill and put your oil return holes in the oil pan, either way dosent matter. i put mine in the back of the block to try to clear the axle a bit more. i should have put them in the oil pan, it was a pain in the ass to drill and tap cast iron.
NOTE: the head thats on the block now was my first attempt at the 16v swap. that head was sold long time ago. but it shows the other spots to put the oil returns off the head)
thats about all you gotta do to the block to prep it for the 16v head. i would highly sugest a good set of forged pistons w/ 4 valve reliefs in wach one!!!!!!! theres some ppl running the stock 2.5L pistons with no problums.