Timing wise, no they shouldn't need any adjustments for unleaded, though if its been re-timed for 95 ron and you put 97ron in, or vice versa it may not run perfectly. From the factory it would have been setup to run with 97+ petrol, and you would hope the car has been owned by an enthusiast who treats it to proper 97 ron petrol not el cheapo 95ron supermarket fuel. Best thing to do is ask the owner, and if they don't know, put a tank of 97 ron in and get it serviced & timed up
The sportline is a special edition, and was only around towards the end of the production line. There were several different special editions, coco channel being one of them.
Brakes are OK, but arn't as good as later models. The main problem is since the servo is on the passenger side of the car, there is a linkage setup which joins it up to the driver foot pedal, if this is loose/worn it can make any problems with the brakes feel worse! New pads, discs, flexi brake lines & fluid will work wonders and should be plenty for a std car. There are several different routes you can take for upgrading the brakes, normaly involving calipers off 80s Audis or similar. Best to have a look thru the MK1 forum for more info!
Sound wise, there are factory 6x4 speaker locations behind the rear door cards and in the front door pockets. Try not to chop up the factory door cards & parcel shelf if you can help it, they are getting very rare nowadays! I'd start with a stelth shelf and larger door pockets perhaps, trying to keep any cutting to a minimum.
I have a pair of 80mm speakers in me dash and 6x9s in a stealth at the back in my MK2 and the sound is very good IMO
The stealth shelf is an important factor in this, it stops the speakers flapping about back there and improves the sound quality no end!
