Assumptions:
L67 from Park Avenue is a Series 2, if so, you will need the accesorry drive, exhaust manifolds/x-over, motor mounts, and possibly the oil pan and oil filter adapter from a w-body L67 car.
55Trucker covered most of the L67 swap stuff, with the exception of the heater core hoses and power steering lines should be from the 98-99 monte carlo Z34/Lumina LTZ with the 3.8NA.
For the manual swap.
I have a getrag 282 behind a L67.
Trans bolts up
Need a flywheel from a 98-02 3.8 Camaro shaved down to to a total of 0.82-0.84 thickness(Find FieroRog on facebook in the fiero groups and he'll sell you one for $300ish).
I would recommend a Spec Stage 2+ for a stock motor or a 3+ for a modded motoer
Axles
- Driver's side use a stock axle from the 1990 Grand Prix
- Passenger Axle - hits the oil filter adapter in stock form. You have 2 options- make a custom oil filter adapter block(have to be thin) and use a oil filter relocation kit. OR What I have done is use the original Grand Prix oil filter adapter, and had a custom axle made. I removed the intermediate half shaft, got another driver's side axle, and used the inner tulip, and the outer axle stub going into the wheel bearing, and then found a 03-05 honda accord 4cyl automatic passenger side axle and used the inner shaft. Put the grand prix outers with the accord shaft. It's been like this for 15,000+miles, behind 300whp motor with no issues.
There is also the interior side of the 96 grand prix you need to take into consideration for the 5 speed swap. You'll need to find a way to mount the clutch pedal as they are different between the 1990 and the 96.