I have a 2000 yr formula 280 br with twin 5.7 efi Mercruisers B3, the tbi 260 hp versions(fresh water, low hrs). I know they are vortec with roller cams. What can I do for a cam without having to cut the the valve spring seats?Id rather not get too deep like removing the heads.
also would I have to have a change in the ecm because of the bigger cams? also what is rev limit on this stock set up?
I know SB prob knows what to do..?

I personally would leave it alone. You are limited to lift with stock vortec heads.

limited gains to be had given your desires to avoid major work.

Unless it's worn out, any change in just a camshaft would be hard to notice in real world application. More RPM would likely require new springs.
Cam, springs and lots of tuning (if it can be done, I don't know anything about TB EFI) on a dyno may gain 4MPH.
Just my opinion, I have not done this combination.

Those motors are identical to the 350 MAG offered that year with the exception of the intakes and MPI vs. TBI. Your best bang for the buck would be to add some dual plane intakes/4bbl carbs. Maybe you could find some busted mills and get the MPI setup off of them to swap out with the TBI setup.

thank you for all the replies. Im going to stay stock for now.