Let's take a perfectly good, classic sports car like a 1987 Lotus Excel SE.
The engine sits in there very tightly.

To make it fit, use the existing radiator.
Hardwire the solenoid so the radiator fans are always on.
Cut some of the fibreglass shell back to allow the manifolds each side to fit.
Make new engine mounts.
Fit a Hilux heavy duty clutch.
Lighten the flywheel.

Fit green front and black brake pads to help stopping.
Remove the fuel solenoid in the boot, and replace with an inline filter.
Make new exhaust pipes running to the Lotus rear ones - throw away the central muffler(shown in image below)
Wire in the new ECU - or, replace the ECU with a 3rd party computer (much easier)

That's Ken at KW Historics without the torch


Then get the car up on the hoist, and make sure the Cert guy can examine everything.
(yes, we got the Cert)
Fit 25 mm adaptors on all wheels.
This makes the car appear to be lower, and more substantial.
There are 11 wheel nut turns to keep the mags on. The Cert requires 7 turns.
The next move will be to measure the space available,
and fit as much rubber
as possible - 285mm.
The nearest tyre size
is 275/40
.