The new hemi is great, but don't forget that its not the price of the motor that is the cost of the conversion.

First, if you want EFI, the OE harness needs expensive mods to stand alone, along with a cable converter for the fly by wire. Otherwise its carb kits which work great too. If the motor is MDS, that will need to be removed as well. The hemi must use and electric fuel pump also.

Getting it into the car requires mounts, headers, oil pan, sb trans, conversion flexplate and radiator+electric fan. These all add up too.

The transmission is small block pattern, so your BB 727 wont work either. You will also need to convert the kickdown to cable, as none of the OE brackets fit.

If you are confortable addressing these items then go for it. A simple cam/spring swap will net 425 hp easy on a 5.7.