If you can get that engine cheap, go for it. At least one club member has the Z-18ET engine in their 1200.

If I recall correctly, it is similar to putting an L18 in, where mainly you need to make custom engines mounts, pound the tunnel out to fit the bigger trans, and have a custom driveshaft fitted. One problem to think about is which trans it has, some are too long for the 1200. Use the Search box on the left to search for Z-18ET or Z18T or something like that.