I have been working on a few V8 build recently and have decided not to rebuild my legacy back to the 2.5L Turbo but to swap it out for a 6.0L V8.
We are building everything ourselves and are working on a V8 Miata at the same time.
The engine is going to be an Iron LS2 or LQ4 which will have headwork and cam done to produce around 450 rwhp. The transmission will be a T56 6-Speed.
The car will be RWD due to space constraints and will fit what I need it to do. I am going to run the GM ECU and interface it to the Legacy cluster.
The front accessories are from a C6 LS3 Corvette to save space.
If you want to see quicker progress buy my stuff haha

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Here are the specs on what I have so far:
2003 LQ4 6.0L Short block with dished pistons
2006 GTO Front Sump Oil Pan and Pickup
2010 Corvette Water Pump and Harmonic Balancer
The head will most likely be 243/799 LS2 heads but I may go to LS3 head depending on what kind of deals i find. Once the heads are bought I can decide what direction to go in as far as a cam
The heads will be milled in any case and the goal is to run around 11:1 compression and stay on 93 octane
The T56 will most likely be the CTS-V unit since it has a shifter setup similar to the Legacy and is improved over the F-Body units
This will send power through an LS7 Corvette clutch