[Finster]

First off you need to find out if it has a 25 or 30 inch transom. If it's 25 it needs to be 30.
I agree with you on the HP but those motors are heavy. The HPDI 150 has the same block as the 175, and their (468lbs x 2) thats a lot of weight on the back of a 23. As for the E-tec's, their off the scale, the only thing heavier is a Verado.
My feeling is you can go with the weight of twins providing you have some sort of floatation bracket to offset some of the weight (others will disagree with brackets, but thats another topic). Even with that I think twin E-tec's or Verado's is pushing it.
One thing people need to remember. When these boats/most boats were designed you didn't have these kinds of HP's and all the weight that come with them.
I see it all the time, the brand new rig with an older hull design and two hot & hefty 250 yami 4 strokes running wide open at a 45 degree angle, just praying to get on plane.