It's a long time since I had my RR, but if I recall, I think (let's see how well I do?);
(a) it wasn't a full rebuild, just 'get it going'....and thereafter the G-box/tranny stayed in on removal, so likely the top plates were backed right off or removed and the engine hauled out- so the instal was reversal (engine in with front right plate attached- left one goes on after, then rear top plates go on)
(b) It'll maybe take a coupe of goes to figure out your preferred method