I'm in the planning stages of building a mid engined car. At the moment, well this is the start, i'm trying to work out what caster angle to use in my build.

I plan on using Mazda Miata front uprights so my kingpin angle is set, but what caster is acceptable for a car with a lighter front end than the miata?

As for the particulars on my "new" build (the Eleven project has been shelved), i'm using the Miata uprights (already mentioned), either a Toyota Tercel or Toyota Corolla FWD engine, trans and hub assemblies, and Triumph Spitfire rack (just cause i've got one). The frame will be a basic spaceframe with rather wide aluminum sill sections possibly bonded to it, and the body will be in fibreglass. I'm planning on using an MGB GT front windscreen (have one of those too), so the body will hopefully resemble the Lola Mk 6, or an early Chevron sports racer.

Cheers,
Rod

Castor is a matter of choice.
Racecars have 3-5 degrees and road cars around 6 degrees.
I have a rear engined car and my castor is only 3 degrees, but this is not quite enough to self centre properly.
I would suggest that you go for 5-6 degrees.

I have 6deg in my mid-engine Mini. It's just about right, though I might like just a bit more.

FWIW, the amount that's "right" is totally subjective.

3 -6 degrees is fine for race cars, I would go more than that for road use & good self centring for SVA.