Agree. I’ve looked at those a little and even with $$$ custom cams and porting it’s probably a 450 HP motor. Sky is the limit with boost, but that’s a tight engine bay!
Merc V12 or turbo V8 could be interesting and somewhat “on brand” as well. Would need adapters designed though most likely. I bet that XF Motorsports could help with that though…
I suppose it depends on your ultimate goal. The added cost and complexity (and trading Aston tax for turbo Mercedes tax) ruins the appeal for staying "on brand". I'd be more inclined to source an AM V12 at that point. On the Aston tax subject, Velocity AP did just announce new pricing for their twin plate clutch kit below $3000 (about $1000 less than it has been).
The appeal of the Vantage to me is something that I can drive year round in Southern California so I'd personally like an engine with more reasonable running costs that I can actually tinker with. Similar to the FD and the rotary, I love the way the looks of the Aston but I'm indifferent about the powertrain. Having heard a few Vantage V8s and V12s with aftermarket exhausts, my main gripe with an LS is the exhaust note doesn't fit the AM. One solution to this might be the possibility of fabricating an 8 into 1 exhaust but packaging is an unknown element. However, the corvette guys have done it so I'd say it's possible.
The appeal of the 1GZ is price point as they can still be picked up for 2-3k and I know people have adapted them to Corvette drivelines. Aftermarket support and availability of maintenance items in the states, is slim to none but some 1JZ components can be used. However, as you alluded to, anything north of 400hp would require significant investment for NA power (high compression pistons, custom milled heads, and custom cams), and while I think turbos would fit in the engine bay relatively easily (the AJ37 isn't exactly a small engine), it adds significant complexity.
