My bonnet stay was breaking up at the ends (an earlier owner's poor crash repair I suspect) so, much as I like my coupe looking original, I used gas struts.
One end attaches to the front/lower mounting hole on on the stay's bonnet bracket, and the other on top of the inner wing in line with the back of the brake reservoir bracket. Closed length is 340mm, open is 590.
When open, the bonnet is really stable, and in the closed position the strut is just over centre, so acts to keep the bonnet down.
The only change to the body is the two holes drilled in the inner wing for the strut end mounting.