How much no claims do you have and how old are you?
My fist car was a 1.2 Nova (12 years ago

). I bided my time for 2 years, building up a bit of no claims bonus before changing for an Astra Sport (Whoo!), ran this for a few years and then when I had 4 years bonus changed the Astra for a brand new Puma. This then led onto Imprezas and now the little French clatterwagon.
That's the best advice I can give you regarding the insurance and fast cars. Unless you are rich and can p!ss £1500 off on insurance.
So in answer, forget the engine transplant for the following reasons.
1. Insurance will go up big style.
2. It will make the car more unreliable and therefore more expensive
3. You'll never sell it on for any kind of decent price.
Steve