Alternator packed in! What fits?83 1.8 gti

Hey everyone, first post on here! Ive got a 83 mk1 golf gti that's I've had for about a year now, constantly been changing and adding bits, recently had a problem with start up where it would just make a loud tick when I tried to turn it over and then after a few tries it would work! Anyway, I gave the starter motor a 'light' tap and it seemed to sort itself out! Since then I have fitted vod gauges and got some of the electrics working on the dash again.

When I went to drive it yesterday I literally got to the top off my road and could here a horrible squeal/squeak knocking noise coming from around the alternator, I was sat at a red light at the time and as I was listening to this horrible noise I saw smoke to start coming from the engine bay but it looked like it was coming from alternator side so I quickly pulled over, it wasn't loads of smoke but as if something had started to melt or something fried, luckily my friend was passing at the time so he give me a hand, we started it up again and there was just this horrible knocking noise coming from the alternator and you could see the knock in it, but the main thing is that we could see quite obvious sparks when you looked at the alternator like some looked like they were flying out of the alternator! I'm guessing that the alternator has just given up and with me adding more accessories to the car over time it's just not helped?
I'm hoping it's nothing worse, is there anyway I can check to see if it definitely is just the alternator?
I'm a bit unsure still as to where the smoke came from cause it didn't do it again when I started it up the next 2 times!
So any help would be greatly appreciated, this is my first major problem I've had where I don't really know how to go about it.
My last question is, if it is the alternator, can I replace it with a 90a alternator? And if so would this one be okay?
https://www.ebay.co.uk/itm/371159300029

I had a look on heritage but the one they say I need is out of stock, I did notice they have a 90a one for a t4 I think, which looked like the same fittings but I didn't know if anyone had any knowledge about if any other models will fit?
Sorry for the long post, hope someone can help me out here,  I hate not driving my golf 

brushes are probably wearing out, I would take the brush pack out and check lengths also the brass rings for scoring and see if the bearings are ok, if they are scored then time for a new alt but if they are ok then a new brush pack will be all you need.

you could use a 90a unit yeah but its not really worth it unless you have a massive stereo and/or aircon etc. the stock 65a unit will do you fine, same one as found on mk2 golf 1.6-1.8 8v so widely available

sorry for the longest reply ever, i have been away, anyway i got a new alternator and all is good now (well i say all is good but i have other problems but hey thats what you get for having a 30+ year old car haha!

thanks guys