Physically, they "might" fit. But, all of the computer controls will not match up. It may be possible to swap ALL the sensors from teh 3.4 to the 3.8, IF they fit, but because of the differences in the engines, the sensors may have fits.
The best thing would be to find the appropriate engine.
Check with the local salvage/wrecking yards and they can tell you if any other year/models would have the 3.4 that would fit.
Trying to fit/swap the 3.8 into your vehicle will end up being far more headaches than it is worth and may ultimately end up costing you far more in the long run.