Just curious if these use the same cams/cam specs... as the Mag and HO engines are rated at same HP levels as the Gi and GXi VP's...

Both manufacturers took the stock 496 from GM and did their own thing in terms of accessories, but the internals are the same (cams/etc). It was a price point engine so Merc and Volvo didn't do any digging into the internals. The Merc's were actually rated slightly higher on engine output, 5HP for each model. Software and and a slightly less restrictive exhaust on the Merc side.

Reason I ask is... I see the VP GXi 420hp cam (new) on ebay @ $300 and anything I find that is Mercruiser is $800+.

Looks to me like they are the same camshaft.

I just bought one to see what exactly it is.

Yep, the same core engine.

I had a 8.1 GXi and now have Merc 496 HO's. They couldn't be more different in terms of execution. The Volvo MEFI 4 software was just awful and it just never ran right in the HO model. The Gi was a little more forgiving. The Merc PCM 555 was superior in everyway.

I will likely use a Holley ECU if I cant get anyone to hack my current VP ECU.
Theres a local guy that swears he can do it... but I cant get him out here until Jan/Feb... so I am in a holding pattern right now.

Could be wrong but the 496ho cam is not a GM cam , might want to research it

The cam I found is supposed to be a 420hp GXi cam... so I can only go by that until it arrives.
I will try to put a dial indicator to it to confirm specs when I have time.

so you have a 496 HO cam to go off of? Let me know your findings because I would like to know my self in case I need one.

No HO cam handy but specs are available online. Id need to look... but i think the HO cam is somewhere around 228/236 @ .050 and .510-ish lift.
Ill update later when I have solid numbers... but I expect the GXi cam to be same/similar.

This is what I’ve seen referenced several times on the Merc 496 motors:
Looking for full Specs on stock 425hp 496HO cam