Based on the pictures I've seen in your thread, you already have the G3, why not wire and fire it? Instead of spending the time and money on building another engine, I'd focus on the G3.
In order to make 400WHP with a stock stroke 5.9, you will need a decent cam and some good heads. You will also likely need a set of pistons to get the compression up. Or, you could just get a stock magnum and throw a supercharger on it and hope for the best.
I've got a soft spot for the LA engines and mine runs pretty damn good. However, I've finally made the decision to go with the G3 and will be moving to that platform soon. I also decided I'll never buy a carburetor ever again after I converted my LA to EFI.
