^ Certainly can. For example, my Mk1 1.4RT the brakes are spongy as everyone knows and not the best, but they are Lucas Calipers which are better than Bendix.
Anywho, you can grab yourself Mk1 16v calipers for the front (with carriers and bolts) for like £30 - £40 second hand quite easily and then fit standard Mk1 16v discs which are like 258-9mm in diameter and vented and then of course the pads.
All can be done yourself and should really help the braking. I'm still in the middle of doing mine, got one more caliper to finish spraying. If you want a good place to buy the std. discs and pads then look here,
https://secure.gsfcarparts.com/shop/
Discs are like £25 and pads £15 roughly. But a 16v setup is best bet, don't just upgrade the discs on std. Mk1 calipers.