Been done, we\'ve been through this conversation before, but it probably got deleted in the big crash earlier this year. I\'ll dig up the link to it, but here\'s the gist of it:
Need to drill and tap an extra hole for the tensioner. Need to find some head bolts, or drill and tap your block for the larger DE bolts. Need a longer timing belt due to the taller CA20 block. Need a custom crank pulley, because the snout on the DE is larger. Need to use the DE engine managment, as they use coilpacks instead of a distributor.
Can be done, has been done, but it\'s a lot of work, and in my opinion, the CA20 bottom end is kinda weak unless your planning on upgrading the bottom end with some upgraded rods and forged pistons (which would again, have to be custom).
Would be cool to see, but I\'m just not sure the extra .2L of displacement is worth all the custom work.
Oh, and BTW, it\'s been done in a Pulsar, not an S12, but should be more or less the same, except that you need a RWD intake manifold to face the right direction.
Good luck.