It all depends on what you want to do. First the 3.4 DOHC will NOT fit, even in my X-11 (unless you want to be driving literally from the back seat. Those motors are at least 6 inches wider than the 2.8/3.1. Your best choice would be 3800SC or the caddy 4.9 v8 (not so stealth). If you want a 4slut in there, get a 2.4l twin cam and replace the head (assuming you can even find a good one) with one from an old Quad Four. I know this sounds wierd but with no other mods other than the head, you will be running around 13:1 compression. If you need other advise, PM me.
Thanks,
Jeremiah

 

He may be referring to a Northstar V8. They are 4.8 liter motor if I am not mistaken.