As an ex-4.8 owner, I'd say that's definitely a 4.8.
Looks like the original Ribcraft console and single jockey, but clearly the rear bench is a later add-on. Looks quite useful - the basic boat is a bit short on seating. Mine just had twin jockeys.
I'm pretty sure that Ribcraft used to rate the 4.8 as 60hp max, but with a statement that you could fit a 75hp if you needed it for regular waterskiing, etc. Can't remember if they stipulated that it had to be a 2 stroke 75. Just had a look at RC's website and I now can't see anything about it.
The under floor tank isn't that unusual, but helps a lot for overall boat balance. Mine had a 60hp 4 stroke and was very stable at full throttle.
They hold they're value well, so not surprised by the price. Excellent handling, dry boat for the size.