4.2???

I have read some enthusiasts talking about taking the 4.0 and stroking it to a 4.2l or higher for better performance. . . has anyone here done this who would care to comment on this?

"No replacement for displacement". There have been several posts about boring out the 4.0, with one claiming you could take it up to 5.0 liters and 400+ hp. Nothing verified, but there are plenty of mods out there.

The mod is to put the crank from the old 4.2 into the 4.0.
The 4.2 had a long stroke, narrow bore. The 4.0 is short stroke, wide bore.
Putting the 4.2 crank into the 4.0 get you about 4.6 liters. There are companies on the internet that sell complete kits for you to do this mod. The kits come with Bigger Injectors to compensate for the larger engine. The stock F/I computer should work just fine. You you need to make appropriate mods to the Intake, Exhaust and Cam setup for the engine to run properly with the increased size. You can use a 2000 or newer intake manifold (has larger plenum and better runners), larger TB, headers and increased duration cam to make up the difference. You will need to make the Torque curve of the larger engine match the same curve of the old engine as close as possible to avoid CEL and drivability problems. When you are done you should expect about 240 HP @ 4600 rpm and 290 ft lbs Torque @3200 rpm. (estimates based on other's experiences).