Oh boy, a brave soul is awakening an old RD-200! First you need to find out if the engine siezed or if it is simply stuck. Cylinder scoring will be a very obvious tattle tale to oil starvation. If the cylinders are clean of heavy galling (scoring) you can try soaking the piston/cylinder interface with a penetrating oil, such as WD40 or the like. After a bit, you can try to carefully tap on the higher piston with a plastic hammer or a wood block. If you get any movement, apply more buster and try to reverse direction by striking the other piston. Work them carefully until they stroke fully. As soon as you can, apply some 2-stroke oil to the cylinder walls and work the engine over by hand until it feels fairly free. But, If you do the above and nothing happens - as if you are tapping on a piece of immobile metal, stop and dig a bit further to be sure you don't have a stuck lower end or primary chain or even clutch/transmission issue. I once unstuck an old bike, when I was a kid, by running alongside with it in neutral, then jumping on and dropping it into gear. It broke free, but it wasn't worth much by the time I lit it off (no compression) GOOD LUCK! Remember to mix your oil with gas until you are sure the oil injection still works.