I was going to do an LZ9, until I stumbled across a deal on a 3.4 DOHC that I couldn't pass up.
Unlike the earlier 3400 and 3500 engines, there's nearly no aftermarket support for the LZ9 (or LZ4, for that matter.)
I think the PCM wouldn't be so bad. The LZ9 was even available with a manual trans, in the G6, so you wouldn't have to reinvent the wheel, to get it running.
If you decide to do this, check out the LGD. It's a Flex Fuel version of the LZ9. It came in about a bazillion Impalas and FWD minivans. It also has the simpler upper intake plenum, instead of the two stage piece that the LZ9 has (unless that's a thing, for you.) The horsepower and torque ratings of the two are identical.
ALL 3.9s have variable cam timing. Also, unless you want the complexity of DOD, stay away from the LZ8.
[This message has been edited by Raydar (edited 04-06-2019).]