The L36 is rated at 205hp at the crank, L67 is 240hp at the crank. But L67s tend to be underrated. They're both solid motors.
As far as swapping an L67, the transmission may be able to hold it. The SSEi did come with an HD version of the 4T65E that'* in your car, but I believe that only means an upgraded 4th gear clutch, differential, and a couple other parts. People who have done hybrid L36 bottom ends with L67 top ends have sometimes used the regular 4T60E or 4T65E, and as long as you aren't beating the hell out of your car every day, you should be able to get away with it for a while. Especially bad would be one-wheel burnouts or trying to screech the tires going around a corner. Much of it would depend on the mileage and wear that'* already on the transmission.
There are mixed opinions on this topic, so some people may chime in here and advise you against mating an L67 with a 4T65E. I'm only saying that some people have done it, and it can be done with success. Just know what you're getting into if you try it.
1997 SE w/SLE package
"White curse? I think it'* more like.... WHITE FURY!" - MyLittleBlackBird