r9, r11, r19 and megane mk1 are based on same platform. The rear axles are interchangeable (and subframes should be too) But only 4-rod axles can be used with ABS sensors without modifications. McPhearson Strut Bearing and most of the other front suspension parts are same on them all.
r19 interrior lamp door switches are the same as volvo 440/460 so are the 1.8l engine blocks.
engines that are the same:
1.4 8v (E6J & E7J) clio, extra
1.7 8v (F3N) from r9, r11, r21, r5
1.8 8v (F3P) from clio mk1, laguna mk1
1.8 16v (F7P)from clio mk1
jb0, jb1, jb3, jb5, jc5 gearboxes from r5, extra, r9, r11, r21, clio, twingo, laguna & megane should fit (there may be differences in brackets).
ph1 dash switches: r21
gauges: r21, clio, r5, r9, r11
heater panel: r21, clio mk1
fog lights: r9, r11, r21, clio mk1
16v steeringwheel: clio 16v & williams
16v seats: clio 16v & williams (chassis brackets need to be changed)