Any modification to a vehicle's frame can weaken it. Welds and joints should be inspected by someone with professional experience to ensure they can withstand the stresses of operation.
You don’t need a machine shop to start. The book focuses on basic tools: A decent welder (or a friend with one). Bike- Scooter- and Chopper Projects for the Evil Genius.pdf
This section discusses the construction of three-wheeled recumbent vehicles. Any modification to a vehicle's frame can weaken it