Are number matching or original components a big deal?

I have an all original 1967 Plymouth Barracuda fastback with 2bbl base with buckets and center console shifter survivor in good shape. The previous owner carved on the volume knob area on the dash to get his stereo to fit. My car lacks VIN numbers on the engine and transmission but are date coded since it was produced before 1968. In fact the VIN number plate on the fender lacks the engine designation letter in the VIN (ODD FACT).

What is the forms opinion on the numbers matching or original parts debate of the vehicle value in its stock state versus modifications? It is no secret the 273 is not a popular motor on this forum. I plan on enjoying the car for a while but will sell it some time down the road but the 273 is blowing blue smoke and blow by is getting bad and I have to do something.

Future modifications could include the 340, magnum 360 and four-speed auto transmission. I understand the value will be directly dependent on the quality of the work performed but will component selection effect the future value of the car?

Specific Questions for the forum

1. Should I just save original 273 and A904 for the next owner or can I just pull the forged crank from the 273 and hold the 920 closed chambered heads and let the rest go?
2. Will it hurt the value if I add headrests (for safety reasons) to the 67 buckets?
3. Besides the fact it cost more to find and build a 340 vs 360 but will the vehicle have more value and buyer appeal with a 340?
4. Do stroked engines turn on or turn off "most" buyers?

I have been struggleing with these questions for a while now. I love to tinker and I feel I have a great platform to make a nice streetcar. I appreciate any advise and opinions you all can provide.

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