Renault
If you haven't changed your engine yet, I would suggest keeping the Renault, as it is a smoother and more economical engine that the Gipsy. You can always change in the future if needed. The airstart system is good if kept maintained. One thing about the Renault, in 0 g situations you can get a rich cut as the needle valve in the carb needs either positive or negative g to work. Have fun, super aeroplane and a genuine two seat aerobatic machine.