Hi. I like the sound of your project. You mentioned upgrading your brakes. Here's what I did to my GT6, and if you want to do this, you'll have to fit GT6/ Vitesse front vertical links, as Herald/ Spity front suspension is different. A lot of people fit the 4 pot callipers from the Ford Capri,(which make a fortune on ebay), but as a cheaper option, get some 4 pot callipers from a LDV van. They are pretty much the same item, and fit straight on. I picked up a pair of nearly new 4 pot callipers a few years back for around £60. I also fitted a bigger servo from a Rover P6.
Anyway, whatever you decide to do, keep us all posted with project.
Steve.