The problem is a lack of timber Paul. All the timber I had amassed for such things has beenNot sure why you need to do this ?
You already show pictures of the rear frame where you can sit on it ?
So why not just build simple wooden frame that can support the front end in the desired position ?
This one is useful as it can hold up a pivoting front end should you nee to work on it ?
Saves having to measure and draw most of an already existing frame ?