*** Red+white are available in 2mm tower type and 3mm. There are none as far as I know that mirror the correct white tint other than those we commissioned specially under the DCC Concepts Brand. We call that white tint "prototype white", and it accurately mirrors the lighting used pre halogen / high intensity lighting, making it right for the 121.
If you want simple reversing lights, basically you need to connect front white to rear red (each with its own resistor) to the white wire and rear white and front red to the yellow. In both cases, the blue is the common positive and is connected to the centre lead.
On these LED, the longest lead is centre = positive, the mid length lead is the white and the shorter lead the red.
all the rest of the lighting should be LEDs too, attached to say the green for the cabin lights, the purple for the cab light. It would be better to use our "flickerfree" lighting on the passenger cabin as the fine PCB strip we supply makes interior lighting very easy.
Martin 71 recently did a 121 - I loaded sound for him. If you PM him he may be persuaded to post a few pictures if he has talen any - his install was a bit extreme with working dash lights as well.
All items mentioned are available ex stock AU and are also available in UK from a couple of retailers who are forum members who post here regularly.