First, yes, that replica is exactly right. Not only were there louvers on the bottom but there was also that large gaping semi-circular opening. Second, TFF is right that there were two basic versions of the SE5a produced, one with a geared engine (which often had problems) and one with a non-geared engine. I think the geared engine was called a Viper Worsley. Conveniently for us modelers we can do the geared version, which allows up to mount the engine much lower.