[Beschleunigt]

Jm993rs,
Looks like a cool project. I would love to do this to my 912 one day as well. There is no cooler 911 than the 911R in my opinion. I looked up a few places where you can source some of the parts that you have mentioned. Remember, there are a lot of places that make these parts. The links below are just what I could find quickly.

Twin plug stuff
Porsche 911 & Carrera Ignition - Page 10
Porsche Twin Plug Ignition Systems Package Parts And Accessories For Porsche Distributed By Patrick Motorsports

911R conversion pieces including fenders
911R Conversion kit

911R Rear Decklid
'65-'68 911 Decklid

More body panels
Getty Design - Doors, Fenders, Hoods, Decklids, Tails for Porsche 911

Fiberglass engine tins
Porsche 911 & Carrera Engine Miscellaneous - Page 6
Getty Design - Miscellaneous Parts, Coachwork, Splitters, Mirrors, Valance, Dashboard for Porsche 911