Welcome. Sounds like a cool project, post it your conversion here, would be good to document it.
You could also start a Barra vs. RB vs. 2JZ "discussion"
Rattle is probably heat shields around the exhaust manifold, but you'll have to investigate. As for sound, it's subjective but I rather proper mufflers/baffles (heavy) than "straight through" cheap light ones, especially on an N/A
Also, this isn't a proper 'for sale' thread so I'll move it.
If you're looking for a price, you can check Japanese auction results. But you're looking at the $10,000-15,000 USD mark
You should be happy that's all you hear.
Just imagine in 1995, all these whizzbang fancy electronic stuff clicking and buzzing away while your neighbours had to pull a lever to prime their carburettor.
Dad bought a Bosch front loader washing machine, it died after 5 years (electronics). The LG one I bought is still going hard after 5 years. Heavy use (6 people in the house).
The "carbon" one is just a top layer of carbon looking fibre (maybe actual sheet of carbon fibre?) on the fibreglass.
Actual pre-preg "dry" carbon requires vacuum bags and an autoclave.
OEM plastic will be more durable than a few layers off fibreglass, look at smashed fibreglass front lips/bumpers versus OE stuff.