Whilst I understand the angle that you are coming from. You need to understand the constraints put on the Author by the publisher.
Anyone who has read the original Ron Champoin book will probably agree that Chris Gibbs has done a far superior job.
With the limited page space that Chris had, it would have been impossible for him to include detailed drawings & dimensions of every possible alternative donor.
Performance figures would have been impractical due to the large number of diff ratio & engine combinations.
The dry weight of the book car is stated somewhere in the book, Kerb weights are dictated by the formula that is applied by the government inspecting engineers, in the uk, Ministry of transport, IVA regulations.
Chris has done a splendid job & gives this forum his full support
Do folk remember how comprehensive Haynes workshop manuals used to be compared with the new style titles that are now more or less, service guides
EDIT
I think the keyword of the books title is quite relevant " On a budget "
This book has been published at a remarkably low price.
What sort of price would a more comprehensive publication command !!??
Not uncommon to pay several hundred pounds for technical publications.
Just food for thought !!