Sounds awesome man, looks like you got all the ingredients! With Solidworks and a TIG you should be set.
The downturn turbo will be the rear, 4-5-6 cyl? I have a 3" DP and its a tight, tight fit.
I wonder if you could carve out the front battery tray, weld in a lip to retain strength (though I don't know how much it provides in that respect) and allow yourself way more room for the rear setup.
Are K03's coolant cooled? Gonna be a hose routing challenge to get it to look neat and tidy, if you're into that kind of thing.
Post up progress, I'd be interested to see it happen!