The short answer is:
Do it right.
The V8 rear end assembly, with gears, will be about $500 +/- for a 1965 1966. You can use 1967 - 1970, cheaper, with later wheels and adapters, but it will still be $400 or so.
Front end, you have to replace pitman arm and everything outbound from it (all steering part, center link, tie rods, sleeves, spindles, etc.) You do not have to change upper or lower control arms.
You will need a V8 drive shaft. There are little parts, like wiring, etc. that has to be changed out also.
It is not a hard conversion, just tedious and expensive, unless you have a donor car sitting right beside you.
Do not put a V8 type engine on 4 lug front spindles. I see too many of those spindles shearing off the right side pin. I do not know why the right side, maybe 50 years of curbs and potholes, or something else. Also, typically with V8 brings higher speeds, and the little drums on a 4 lug can't handle it, so the entire car becomes a parts car.
ed ay +3112
1968 GT500 Arrest Me Red (The Big Boy Toy)
1966 K Code Vert (The K 'Vert)