I dunno if the spinning one is original or not (some says its a french car..),anyway the engine sound is that, also in replica (they usually use small block ford 289,302,351 ..).
If u have heard the Rover engine,surely that will be a little different(less aggressive than this one,but a lot depends from the exhaust).
Consider anyway many owners have more than one exhaust,u can change the "snakes" for road use..or for track-race use..

look at engine bay pictures, that seems not such hard work as in ordinary cars.
From what I know the rover engine was used on the first replicas cause bigger american (more powerful) units gave bigger problem to the chassis (the difference is in the order of 150-200 hp, for americans,and a really stronger torque).
Even from (the few honestly

) I know, seems Rover engine is also more complex and expensive than Ford units.
Probably when all started many used it cause was the best unit available for kitcars,and in the 80s that was a real masterpiece in performaces,surely really cheap for this pourpose in Uk.
With Fords u are also more "original".
The rover 3.5 liters v8 is anyway a good engine,perfect if u like a more cheaper car,perfect as a start (I remeber club member kva rover v8 for sale at 16.000 gbp..that is a TOO GREAT bargain to drive a wonderful car..) and anyway keep in mind it has never less than 200hp,over a car of 1000 kilos, that is a LOT if compared to any production car.
Today there is the possibility to have better chassis able to take even more and more powerful units (many ones have up to 450 hp),also if sometimes this amount of power becomes surely hard to control (geetees do not have antiskid or traction controls..so its all under your feet..)
hope this help
ciao