I have been looking at a couple Gen 6 engines, are the bolt holes in the same place for all the V-Belt accessories? Will the 3groove pulley on the balance bolt on?

I know they is no provision for fuel pump.

I think everything matches except a couple of holes are 3/8 instead of 5/16. I have done that swap in the past and only had to find a couple of bolts as I recall.

yes everything will swap over..

It all lines up. I did a full serpentine kit on a Mark IV block no problems. I don't know about the bolts cause I just replaced them all with new. Other than that it all lines up.

Thanks!

I see no reason to not go to a pair of 540's, the wife will never know the difference

Everything will match up with the exception of having to open some 3/8 accessory holes up to 5/16 as wobbles previously said.

Yes.... but You will have open all the accessories hole to 7/16 not 5/16 it is very easy to do all you need is a cordless drill and a 7/17 drill bit and new bolts. been there and done that for last engine build.

You may also have to do something about your oil cooler adapter and hoses if you are using the stock Mercruiser type.
Gen 4 uses a filter adapter plate with 2 bolts. Gen 6 is setup like a Ford with the filter screwing on to a pipe thread straight into the block. The stock Gen 4 oil cooler adapter will not work with this. You will need a different adapter and oil lines.