3900 Vs. 3600
The 3600 is a more powerful engine, it also isn't an engine used in the W-body Vehicles. So finding mounts that already exist for it would be close to impossible. you would have to fabricate, but seeing as how you are doing an engine swap, you where going to have to do that anyway.
The 3900 is found in both the G6 (LZ9) and many W-body vehicles, so the mounts will be easier to come across, along with many other potentially required components. This engine also has displacement on demand in Impala's and Lucern's (LZ8). Match that with a 6speed manual geared properly and you will be looking at very impressive fuel economy.
Now if you are looking at the numbers on paper....
depending on vehicle application (and tuning)
3600 V6: 252hp @ 6100rpm, 251 lb/ft torque @2300 rpm 10.2:1 compression ratio, engine weighs ~370lbs (the L67 engine weights ~390lbs)
3900 V6 (LZ9): 240hp, 240 lb/ft torque
If you want the best 3600 V6, you should probably be looking at the Cadillac CTS 3.6L . It's direct injection and might bolt up to the G6 6speed, but I'm not sure on this. It's hard to tune and get a wiring harness for it to work. I don't think the mounts will work without fabrication (RWD engine). And it's the only 3.6L still being made.
302hp @6300rpm 273 Ft/Lbs torque @ 5200rpm
