Good decision not to go with the Westfield for a targa car. There is little to no chance that you would survive a high speed crash with the low side walls.
Also the visability is quite poor when your low down, approaching a bend it can be difficult to see over and around it.
you chose the safer option.
MC days, hillclimbs and sprints are perfect for the Westfield. but a full roll cage is best for Targa.
All the best.