Hi I am hoping someone out there will know this:

I am installing a 4 speed manual trans into a w123 chassi but one day I would like to replace that with a 5 speed manual (God willing).

My question is:

Could I simply switch out the 4 speed manual trans with a 5 speed manual trans? Are they both the same length? Would this effect anything with the drive shaft or rear differential? (ie drive shaft length or gearing in the dif). Also what about clutch petal placement etc - those would remain the same, correct? Are there other considerations I am over looking?

Any help would be really appriciated (since I have grown restless looking for the elusive 5 speed manual trans for these car but would still dream of owning one eventually)

Cheers!
-L