Replacing rods

If its knocking, the only way to really find out is to tear it down and take a look.

It appears that you may want to swap from a 6 cyl to a v8? If that is correct, you are looking at upgrading the engine, front suspension, tranny (at least bellhousing), probably front brakes, exhaust system, and rearend work (if you also want a 5-lug system all around). The costs depend on where you're getting the new parts, level of conversion, and who's doing the work. You can easily spend $10k, or get by on $3k.

I know this isn't much help, but it should help you focus on what you want to do.

The sounds could be many things. Are they coming from the valve covers, the intake manifold, or the oil pan? We should start there

Very likely, knocking rods are also accompanied by crankshaft damage. In which case, replacing the rods alone will soon find opportunity "knocking" again reminding you that you should have had the crankshaft repaired/replaced also.

Sorry, I have lots of experience that supports my view.

Troubleshooting a knock via the internet is a little tough. Whatever it is, the motor needs to come out, come apart, then you can accurately assess your options.