im lookin at a 4.3 . i got some ?

im going to look at a 4.3 for my mazda.he's asking 350. for it but im gonna try to bring him down to 300. and i found a 700r4 for a good price. do i need a custom driveshaft and rearend or can i use the stock rearend with a custom driveshaft.and how much power do these v6's make stock,and does a shift kit really help an automatic