Body and chassis work almost always comes first. There's a good reason for that. Salt, damp lock ups and British weather work their way into sills, floors and chassis rails. This happens long before the engine even gets a look in. On the Big Healey body, that usually means the front and rear chassis members, the sills, the boot floor. Door skins and wing sections often need attention too. They take the brunt of stone chips and careless car park scrapes across decades on the road. It's not glamorous work. But get it right and everything you bolt on afterwards actually stays put.
Once the shell's sound, the mechanicals start calling for attention. Brakes sit near the top of that list. Wheel cylinders, flexible hoses and master cylinder seals perish with age, even on a car that's barely covered any miles. Rubber doesn't care how many miles are on the clock. It just cares how many years have passed. Cooling systems follow close behind. Water pumps, hoses and radiators show their age either way. It doesn't matter if the car's been thrashed on B roads or left parked under a cover for years. Suspension bushes harden and split too. Once they go, that famous Healey handling starts to feel vague instead of sharp.
Electrics tell their own version of this story. Wiring looms perish where they run near the exhaust or through the bulkhead. Old bullet connectors corrode until they stop making a clean connection at all. Fuel systems need the same kind of care. Tanks rust from the inside out. Fuel lines harden and crack, and carburettors gum up if the car's sat unused over a winter or two. None of this points to a badly built car. It's simply what happens to any machine built before synthetic rubber and stainless steel became the standard.