IMO not worth the effort to do a V8 conversion with the Rover / Buick V8 unless you are prepared to spend lots of time, effort and money getting the specialised parts required to get useful horsepower out of it.
For the same amount of effort, the small block Chevy slips in a treat, is well documented, has aftermarket installation parts available to buy rather than fabricate and has power potential only limited by the depth of your pocket...