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@Snydert59. Your '66 MGB of BMC project looks very interesting and seems to be a full built quality job. Does it still have the OE 1.8 I4 engine (18GB/UH, 3 main bearings only)?
The k24 factory has double the hp but 30ft lbs of torque less than the flathead six...This will be my first attempt at putting a Honda engine in anything.
When I see your '51 Plymouth I hear a Chevrolet Stovebolt 261 (4.3 Liter) inline 6 or an AMC' 258 (4.2 Liter) or AMC's 282 (4.6 Liter) inline 6 engine. Something with a huge displacement and low revving power as well as a noisy drivetrain. More modern and quite more tuneable in NA would something like, GM's daughter Opel had once a very nice inline 6 engine, the C30SE with an 4-valve head, which could be bored up to 98 mm, in a 98x88 I6 layout it made 4.0 Liter and up to 400 hp in NA mode in a more racy specification, 260 hp was quite easy with them. Of course all of them are more heavy compared to the Honda K24 full aluminum alloy longblock, but all of them provide the low speed torque you need to move that chassis adequate and nicely with the sound it should have.
I live around a corner where about 3 to 10 AMG flat-plane V8 engines pass through their commute to AMG headquarter. That flat-plane V8 crankshaft sound is amazing, when they babble around the corner and WOT after it shortly to accelerate, this is wall vibration causing and makes me smiling ear-to-ear. Imagine, AMG is or was trying to sell I4 engines in the E-class, the sound is...you may need to be born in the 2023'ies to cope with it, I can't cope with that. The chassis and the sound has strong connection for me, characterizing the soul of the car. Think about the characters of e.g. the Wulf gang of the film "Warcraft, the beginning". What would you think if they sound like they had inhaled N2O, like kids, this would be like slapstick, wouldn't it?
I wouldn't go that far thinking of a Toyota 2JZ or BMW M55, these are higher revving low displacement engines with no character what a Plymouth would sound to me. BTW, I assume the enginebay is too small or at least challenging for an 90° V8, which would be a nicer sound option. Hence the I6 approach is the thing I would hear at this engine. I myself have a strong connection to the I4 route, especially the I4-2-Liter-NA-engine, which has the best ever sound for those European chassis I grew up with: Opel with the Corsa, Manta, Ascona, Kadett and so on. All of them had I4 base engines and weigh around 750-1050 kg, market accepted power ranged from 60 to 150 hp. Implementing a stock C30SE engine (204 hp) into an Ascona chassis was like a rocket and an amazing sound upgrade. BTW, the Opel Ascona B in the I400 version was won the World Rallye Champion in 1982
I4 engine (i400 type) with 2.4 Liter and around 340 hp in the top version.
Imagine the Opel Corsa weighed about 730 kg with some weight mods and with an I4 engine like the C20XE (150 hp stock) it was a rocket in the 90'ies and sounded like a real adorable car.
Opel Corsa GSI chassis with an C20XE engine (2-Liter, 4-valve head, 150 hp stock).
These cars sounds like the look like.
Just my two cents.
I understand the K-series approach, it's available, cheaper, easy, huge aftermarket, and so on, beside my concerns
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