So I'm not entirely sure if I should post these questions here or in technical, but here goes. Q1. I've noticed in pictures I've seen of various crabs from around the world that the speedometer is different. Sometimes it's just in miles, sometimes it's in miles and kilometres. When I eventually get a crab, if it has a miles only one, how difficult would it be to source a kilometres only or a miles & kilometre one & how easy is it to swap it out ? Q2. Also, people on the Aussie 1800 Google forum have said that in the MK3 crabs rod gear changes were used as opposed to the cable changes we had here in the MK1 & Mk2. Does this only apply to the manuals or the autos as well, and how easy would it be to source parts and change out ?
I can't really answer the question. The Oz cars differed in many subtle ways from the UK cars - some of the Oz members will be able to answer the speedo question more exactlty. As over here, I imagine that stuff pops up on eBay and similar sites from time to time and you would need to maintain a watching brief see what appears. Actually removing the speedo is a complete cow for access. It may be easier to take the entire dash off its mountings to get access from the rear.
I'd leave the gear shift absolutely alone. Both are pefectly acceptable unless you want to drive a racing car, and this ain't it. The cable change doesn't want to be rushed but is very positive to use. The rod change is quite "snappy" but lacks the mechanically solid feel of the cable one. I'm not sure that the two assemblies directly interchange, either. You need to get yourself a car and see what you think after using it for a while.
I have owned two (Mk111)cars with rod changes and several others (Mk1 and Mk11) with cable change. As other have noted, the cable change is very positive if a little slow. The rod change does feel slightly rubbery and less positive in comparison but not that bad and maybe a little quicker. I believe there may be some differences in the selector forks, so I am not sure if the conversion from cable is as simple as it may appear. The exhaust down pipe on the rod change cars has an extra bend to avoid the rod change mechanism so would probably need to be changed. The main advantage I found for the rod change is that it does not leak oil unlike the cables, although there are a number of fixes for the latter.
As Chris has pointed out you may feel that the car was built around the speedo if you want to change it. Definitely not a quick job. I am now driving cars with speeds only marked in km/h although I was brought up with mph. I find it quite easy as far as speed limits are concerned as I only need to remember the following approximations:
50km/h = 30mph (31.25) 80 km/h = 50mph ( 50 ) 100 km/h = 60 mph (62.5) 110 km /h = 70mph (68.75)