The problem is that SLE 88/89 are Streamline points and so most would use Flexible track with it, however, using Peco Settrack, you can use ST238 to bring it back in line. It would however bring the tracks closer than the normal track centre for Settrack and Streamline, which could be an issue in some cases.
Putting an ST203 between the SLE 88/89 and the ST238 would take it to Streamline track centres and using three of them would take it to a little more than Settrack track centres. If you use two it will put the track centres between the those of Streamline and Settrack.