Looks really nice, like a vintage 50's or 60's sports racer. I think here in the US a Spitfire or a TR6 might make a better donor car. Heralds may be more common in the UK by over on this side of the pond they're a lot harder to come by. A Mazda Miata drive train would probably be an even better choice for the donor, although if you did go that route you may have to fab up a chassis for the car. I like the period egg crate grill.
I just noticed that they will sell a turn-key car starting at £5,500! Quick conversion and that's only $8,850. Not a bad price for a car that looks like that.