How much bike to use

Today's question is: do I cut off the entire rear triangle of the salvage bike, or do I only use half of it? That steel is heavy! Moreover the connection into the main bike is tricky, since I foolishly did not leave a long tail on the lower pole, and the bracing poles interfere with connection parts.

I have long tails on the upper two bars. This is what I leaning toward: I will use half the lower bar of the triangle, connecting the cut-off ends to a bamboo fork I can splice into the main frame. I will use the entire rear bar of the triangle, to have the mounting space for brakes and other items. The tails of the upper bamboo can make nice lap joints with the rear triangle bar. The bamboo, with a little shaving, can fit into the cut ends of the lower bar. A little diagonal bracing and this should be a strong mount.