I think bekkers sells a stroker kit for the w124, you will have to call them and find out, as it is not listed on the site. That would probably give you 250hp or so. Beyond that, saw off the intake scoop that connects to the air-box... that will give you a little more performance. Another option is building your own supercharger for the car, which would be extremely time consuming. Mosselman also sells a bi-turbo kit for the m103 engine that is supposed to put out near 300 hp. It costs 6k though... plus installation.