There's a lot of room outside of each engine, but it's very tight at the inside/back of them. (and the actuator makes it worse)
There are probably 5 different cowling designs in the various 280/290/SS/BR's. I have the curved rear seat, the base of which is bolted to the floor and sides. When I do serious ER work, I remove it, which opens everything up and makes a big difference in accessibility. That's not necessary for routine maintenance btw. Batteries and fluids for trim, tabs, oil and steering are all accessible when the hatch is lifted.
The battery config on mine is clever: a dedicated and switched starting batt for critical systems and port starting, and then 2 more are switched 1/2/both for house and stbd. On top of that, I can parallel port and stbd if necessary. (SeaRay's Emergency Start)
The extended swim platform was optional, at least in the 90's. That puts the drives right at swimmers feet, esp with twins.
The cockpit sink console was reduced in size for the 2000 model year. That provides for some more floor space, but I like the large storage area and countertop (under which can be an optional fridge).
I have carbed twins w/ Alphas. Twins are great, carbs and Alphas not so much. However, I can put an adult in every seat on this boat (and that's a LOT) and push the throttles fwd and she'll come on plane like a jetski. Another bonus to the twin config is standard 4-lever Morse controls (racing style). Every single I've seen has had the combing-mounted Merc lever.
The ER scupper design is poor, and that's one of if not my only complaint about design. Water travels down the sole and under the seatbase cowling, where it is supposed to fall into a gutter and then to out the side scuppers. Heavy rain or a big wave (BR!) will overfill the gutter and put water into the bilge. That water also travels past the screws that hold the seatbase to the floor, so I always tell people to check for softness in the sole around those screws.
'97-'99's were covered in stripes and graphics that IMO, were ugly evew back then. (3 shades of brown with some gold thrown in... ah, the 90's...)
I removed all the stripes this spring. I plan to replace the stripe above the rail, but I'm not sure what I'll do on the hullsides.