Filling the gap between cars and motorcycles, trikes are one of the most unique kinds of transportation on the road today. There are two basic types: tadpole and delta. Delta trikes are the most traditional arrangement, utilising two tires in the back with a motorcycle front end. Old-school trikes utilised a Volkswagen engine, transmission and suspension mated to a motorcycle front end via a section of tubular frame rail.
Acquire a running 1995 to 2002 Lincoln Continental. You can think of this car as a kind of trike-in-a-box; it utilises a 4.6L modular V8 capable of putting huge power to the ground, an A4XN four speed automatic overdrive transaxle configured so that the axles exit behind the engine and a strut suspension that will easily adapt to rear-drive usage. GM fans should consider a Northstar-powered Cadillac from the same era, which is almost identical in most ways to the Continental.
Remove the car's engine, transmission and suspension by unbolting the front subframe and removing them all as a package. Take care to not damage wiring harness, computer, shift linkage, throttle linkage or suspension components, since you'll be reusing most of them.
Build a new lightweight subframe from tubular steel, incorporating a new set of struts mounts to support the struts. Tie the tops of the struts together with a strut tower bar for rigidity. You can replace the power steering rack with a toe-adjustment bar similar to those found on Corvettes.
Build the remainder of your frame. Design it so that the radiator sits in front of the engine and place the seat about six inches ahead of the radiator. Place the front fork tube mount at the angle required. Design the frame so that you can place the brake master cylinder assembly in the area between your feet, the battery behind the master cylinder and the fuel tank between your knees.
Install the widest front forks that you can find, and utilise a super-wide motorcycle tire designed for the rear of a sport-bike. Connect the brake master cylinder to the caliper on your front wheel by way of a brake proportioning valve to perfect brake bias. Connect your foot brake to the centre-mounted master cylinder with an offset linkage. Fabricate a throttle linkage and throttle pedal on the other side.
Connect your engine and transmission to the computer wiring harness, and wire the rest of the trike's lights, gauges and ignition system. Wiring can be a complicated job, but in general you'll want to install the electrical system in this order: main fuse block, engine, chassis lighting (brakes, headlights and indicators) and gauges. If you're unfamiliar with automotive wiring, then consider purchasing a pre-engineered, universal race car wiring kit complete with colour-coded wires, wiring harnesses, fuse panels, switch gear and instructions.
If you don't have extensive experience in designing and building tube-frame chassis, then you might want to consider farming this job out to your local race car fabrication shop. Tube frames are tricky to design and build, and doing it wrong can and will result in disaster. If this is your first tube-frame project, then you need to enlist the help of an experienced frame builder and read both "Chassis Engineering" by Herb Adams and "Race Car Engineering and Mechanics" by Paul VanValkenburgh. Drive carefully. Delta-trikes are popular, but they're inherently unstable while turning and braking. Keep the weight over your trike's front wheel as close to one-third of the total vehicle weight as possible to reduce understeer while turning, and keep the centre of gravity (vehicle mass) as low as possible to reduce the odds of flipping over while turning.