I have a 2000 bonne Ssei, all stock. Has about 70,000 miles on it. Could I swap in a 4.6 Northstar from a latter Bonneville model or would a 2000 year 4.6 from another H body car work? How many mods would be needed

A few have proposed swapping a N* into one. I'm not sure if anyone has. The L67 motor would be an easier swap with potential for more power.

Don't I already have that, the 3.8 supercharged?

Yes you do. But you can do more with the L67. The N* has no real mod options. You would also need to look at swapping the transmission from the 4t65e-hd you have now to a 4t80. Not sure what would need to be done about axles and hubs. There will be wiring to change. Not sure how the N* PCM will match up to the 2000 SSEi setup. Anything can be done, just a mater of time, money, and knowledge.

So with the L67 how could i get it up to sounding like a V8 like a N* and the hp

Your not going to get it sounding like a V8. There will always be a mid range rasp. But with ported intakes, a good cam, headers, and open exhaust you will get a good deep tone and idle and low power acceleration. A supercharged engine also has a lot of torque. 300hp to the wheels is very possible, and even more.

if i do all that ill prolly be around a grand

If you put a cam in your L67 it will sound kinda like a v8. But not really. Go to YouTube and searched calmed GTP or Bonneville with the l67 or 3.8s.

Yeah Ik what a cammed will sound like, well thanks

I say stay with the 3.8. They' re moddable and reliable and a ton of fun with the mods Danthurs listed