Hello Marconi,
The exhaust is filled with stainless wire wool. So not empty.
I use the gearbox from a porsche 911. Old type 901 gearbox.
The wheels are replica's from Tony Castle Miller and are 5,5j in the front and 7j in the back.
The tyers are Dunlop racing classic 4,50 CR65 13 in front and 5,25 CR65 in the back.
Ik hope I helped you with this info.
Are also building a OT1600?
Groet,
Fred