The choice of donors is huge. Any rear wheel drive, front engined car will do for a Locost (this doesnt have to be the case, but its easiest). If you have the time and patience and skill you can do anything. People have used the Mazda MX5, motorbike engines, the Rover V8, Ford V6...and they will all fit with some modifications to the chassis.
Lets deal with the 3 main (common) donors in turn, infact in the order I considered them…
The Mk1 or Mk2 Escort
If you can find one, you want one with good mechanicals and rotten bodywork. But since so many people have built these cars in the past few years there are very few of these around. There are however several out there, so just keep an eye out for one if traditional Locost is your chosen route. They came in several 'flavours', 1.1, 1.3, 1.6 and RS2000, the 1.6 probably being the most popular for use in the Locost. The crossflow engine is pretty decent (was even revamped and used in the Ford Ka), it is easily tuneable and the spares/tuning parts are easy to get hold of.
Pros;
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Can stick closely to the book
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Pretty much all of the parts can come off one car
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The crossflow engine is very tuneable and more refined than the pinto found in later Fords like the Cortina MK4 and Sierras.
Cons;
The Mk3, 4 or 5 Cortina
There are several of these around at better prices than the Escorts, and in pretty good mechanical condition for how old they are. There were many different engine and gearbox combinations in the Cortinas. The early ones had the crossflow engines, the later ones had the pinto. The rear diffs on the Cortina are available in different ratios to that of the Escort. Which will give better acceleration and lower top speed IIRC (all depends what you want...IMO acceleration is better)
Pros;
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Again all the parts can come from the one car (except the steering rack as it is too long to fit the front of the car)
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The book chassis can be easily adapted to take all of the Cortina stuff, some of them even had the individual dials which look nice on the dash of a Locost.
Cons;
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The track of a Cortina is about 4" wider than an Escort. While at the rear this wouldn't be a problem, the front would either need a redesign or go back to the Escort rack.
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The later Cortinas had the pinto engine, which requires modifications to fit into the chassis (shortening the sump and modifying the rocker cover). Although in 2ltr form the pinto would give quite a respectable power to weight ratio.
The Sierra
These make powerful Locosts (especially if you use the 2.8 version or the Cossie), but come with many complications. All of the Sierras were IRS and powered by either the Pinto, CVH or DOHC. Avoid the DOHC and CVH if possible, they are not as tuneable as the Pinto. It is of course possible to use the Sierra engine and box but use an escort rack and live axle. The great news is some sierras came with the 2.8 litre engine...anyone up for some serious power??
The Sierra is my choice of donor, as its cheap, easy to find, easy to tune, and easily adapted for use in the Locost.
Pros;
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You can get spares for them from literally anywhere
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There are 100's of them out there rotting away, but with mechanicals that are OK, avoid the thrashed ones, even if you are considering an engine rebuild though!!
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The option of the LSD if using IRS is a good one, but leads to problems.
Cons;
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The pinto engine will not fit as standard into a book chassis; it is too high, needing modifications to the sump and rocker cover. Or modifications to the bodywork.
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The front uprights need modifying...or you still need those elusive Cortina items!
