I had this opportunity for my B-body. A '69 GTX. That's a nice driver quality car. But not even close to numbers matching. Period correct 440 of lightly upgraded performance. 4-speed Dana rear. Car is D32 coded for an automatic. With interior not even close to fender tag. Thus a very decent candidate for performance upgrade.
I had the opportunity to buy a just off the dyno 6.4 non supercharged Gen III at 545 HP. So the choice? Pull a very good running '68 440 engine at 425 HP for $14k. For this engine. I would need to upgrade K-frame. Clutch/bellhousing. Electrical. Fuel system to EFI. Radiator plumbing redesign. And that's just what I can think of off the cuff?
My Answer was "Thanks, but no thanks. I could spend that $14k on aluminum heads and intake upgrades and cam. A833 transmission replacement for ideally a A855 5-speed. And save all the support hassles and costs to accommodate the newer technologies. And blow that Gen III off the road.
The only engine upgrade I would consider? A Gen II hemi. (A real hemi)
Just my opinion of course. And a quick walk around vid of the subject vehicle below.
That story makes me ask the question; what do you get with a G3 Hemi that you can't with an LA?
Here's what I could think of:
Cross-bolted main caps
Raised cam and better (not perfect?) pushrod angles
Direct shot ports due to opposed values rather than inline
Valves move away from cylinder walls instead of towards them
VVT (on '09 later motors only)
Cam position sensor on front of cam instead of all the way at the other end
Crank driven oil pump
Question is, how much do any of those impact a build? I would guess if you don't go over 600 hp, the stiffer block and increased main cap bolts might not make much difference? If the heads flow similar numbers, will it matter that the LA shrouds the valves as they open but introduces a swirl to the mixture? Crank driven oil pump removes twist from the cam, but how much does that play into things?
Questions I can't answer. Does seem to me that the G3 Hemi is more efficient than the LA in regards to MPG and power, but is that only due to tuning, airflow and compression? Don't know.
For me, the fact that someone with some computing power behind them sciences out the 5.7/6.4/6.2 makes me think they are a better all around motor than the LA. If I was shooting for 6-800hp, that (I think) is a no-brainer, but for my mild goals the differences are probably minor enough to not make a big difference.