To answer StorminNorman's question, no, they're not. Your 450SE is a W116 chassis/body style, but it has an earlier iteration of the M117 engine. Your W126 420SEL has an M116 engine (a development of that in the earlier 380 cars). The old chain rails in your 450 would be transferable to a 500 or a 560, which are later M117 engines, but not to your 420. The suggestion by Tomguy is an interesting idea, but won't work in your case.