If the 86' was making 40-45 hp way back then, how much hp can be achieved today?

I do not know how much more power can be found in these old engines.  How much more time do you want to invest in looking??  How much money are you willing to spend on these old engines.  The reality is:  This old engine cannot be developed to make the kind of power and have a wide power band like the modern two strokes.  The technology is just not in the ports, reed, crankcases etc on these 85-86 LT 250s. 

We have to start with the port technology that Suzuki cast for us 30 years ago  Some port designs are superior to others.  Port technology has progressed a lot in 30 years.  Pipe technology has progressed a lot in 30 years but we can only do so much with pipes on 30 year old port technology. 

If you were to increase the displacement to over 300cc, it will make a little more power if you spend the time to simultaneously develop the ports and pipe together.  I have not had very good results trying to build killer pipes for engines that were developed for other pipes on the market.  We usually have to try different port modifications when trying to use some of the more modern pipe technology.

I would be leery of installing a big bore kit in one of these 85-86 castings.  We had cylinders splitting in half when these were just real good running 250s.  When you start putting big bore sleeves in them, the castings become much weaker because of all of the metal that has to be remove to make room for the big bore sleeve.  Weak cylinders are more flexible after the big bore sleeves are installed  and are also more prone to head gasket blowing problems. 

Current state of the art 125 two stroke road racing and shifter kart engines are making almost 60 hp.  The CR250s that we built for the shifter karts and micro sprints in the late 1990s were a little over 70 hp.  500 cc two stroke road racing engines were making well over 220 hp when the FIM abolished the class and replaced it with big multi cylinder four strokes.

There is more to porting that cutting the ports to a popular port timing spec when building a two stroke.  The port timings on highly developed two strokes are about the same as they were in the late 1960s.  Yamahas 1968 TD1 250 twin road racer had around 35 to 40 hp.  30 years later Yamaha's TZ 250 road racing engines made around 80 hp with similiar port timing.  Around 2005 the Rotax/Aprilia 250 road racing twins were making 115 hp.

There are a lot of builders around the globe that can cut the basic port timings and reshape the port tunnels needed to make the engine breath at the higher RPM.  There is a lot more to designing pipes than entering the port timings of your engine into a pipe design software package or downloading a pipe design app for your phone.  There is only so much that can be done to these old  engines regardless how much money is spend testing and developing a new pipe.