As far as the Optima battery is concerned, I've had one on my BJ8 for the past 2 years and haven't given it a second thought.
I build a box and covered it with black vinyl. It fits in the battery tray and is covered by the vinyl battery cover that originally came with the car. The box and cover fit the look I remember seeing in a number of Healeys back in the early ‘60s.
A friend purchased a tar-top cover from Moss for his Optima. It appears very realistic, and only appears to have one slight difference. The terminals of the Optima battery are further away from the battery’s edges than on a true tar-top.
All the best,
Ray (64BJ8P1)