sadly V8's are the last choice for most pakistanis since they either want economy or some high revving jap cr@p.
like redbull_ar said the easiest to find will be a cruiser V8 but even that will be a real hard task. i shoudl point out that those engines are "underbuilt" and can take boost so you misght want to consider supercharging or light pressure turbocharging the blocks as well.
there are many mechanics who can work wonders with such cars (muscle). there is khalid ustaad in westridge, rustum near choor chawk, jaan motors (the workshop), liquimolly in I-10/3, etc..
good luck (Y)