Whats the spec of the car, what suspension, brakes, fuel system, guages, tanks, hoses, exhaust and so on, what wheels do you have, you will need to budget for that also and that's realistically at least 1/3 of your budget already. Speaking from experience if you haven't allowed for those bits already i'd take half of that 6k figure for the engine and use the rest to buy all the acessories, or you'll end up with an unfinished car or something that is shit and unreliable to drive.