6-7k will get you a good 400 conversion

BUT

if i had 6-7k to spend i would save 3k and spend that on brakes/suspension/diff , then spend 4k having a 360hp engine built.

if you go for something along the lines of T34/ .63 , BD14 inlet , light lues , WRC gasket youll have a some fun rather then getting the engine and not doing brakes and suspension then struggling to keep it on the road

HTH