Buy it, restore it, race it. Firstly there is no such thing as a YZ460, I think you mean the YZ465G and YZ465H sold in 1980 and 1981. The 1981 model is better because it has 43mm forks. Much of the engine is the same between the G and the H, but the frame and suspension are different. While this will feel a bit like going back to the stone age compared to your RM, the YZ465 was considered an excellent bike in its day. They are very competive in historic MX today, and make a good off-road/desert bike etc. Stay away from the later YZ490s they were a handful. The headlight concerns me, to make sure you are not looking at an IT465 check the serial number with a Yamaha specialist like Speed & Sport.