One more TOS-movie era volume comparison...
Enterprise-refit ~238,000 m3
Reliant ~ 254,000 m3
Enterprise measured at 1000' x 465'. Reliant beam matched to 465' with a length of 791' (241m). As I suspected, that large back section gives her alot more volume to work with. Nacelles are rough placeholders, but mostly same for both Enterprise and Reliant (Reliant's nacelle lacks the bottom blister.)
Now how those power transfer shafts go from the engineering section to the nacelles on the Reliant - that's would be a challenge to map out