is the engine harness between the XLR and the V the same and the PCM are they the same.

Here we go again . . . Major XLR mods are few for a reason.

There's no PCM in the XLR. It uses an ECM. This is the least of your worries. Your sanity is important.

I'll save you a couple of thousand dollars right now: Take half of the money allotted for this project and send it to me. Take the remaining half and invest it in lithium battery manufacturer stock. You will not have wasted a single penny.

Or . . . Sell your XLR and use the project money to buy an XLR-V. Again, you will not have wasted a penny. A "V" is a lot more than a powertrain.

You could also try the XLR Excommunication Route (and save a bundle in the process) by installing the (required) power dome hood and "V" logos, and wheels, and brakes, and . . .

If you really want to try this . . . keep saving. Some dreams turn out to be nightmares. This may very well be one of them. Buy a 2004 XLR Shop manual and a 2006-9 XLR-V shop manual. This is the first path to "V" Enlightenment. Compare pin-outs in schematics. Compare part numbers online. Price said parts. Know before you Go. Save your money. --And your sanity.

CC :nono