Starting at the top. 10 quarts are always desirable , but yeah you'll need a longer pick up. Some 10 quart pans come with longer pickups so be selective. The motor mounts 3. Should be ok if you're not going over 450 horse. But four points would be the way to go if you're pushing bigger horsepower. Why would you want to run over the transom headers? You say you don't see yourself Hot Rodding in this Cruiser so logs would be the way to go. A 750 Holley should be ok , you're not hot rotting.

...I'm going to be dropping in this 460 I picked up into my 1975 Wriedt Montara...how important is it to swap from the 77 truck pan, to a 10 quart pan?

The front sump Cobrajet and Marine pans have a slosh baffle in them and you ought to be fine if you are using one of those pans in your cruiser. But if your front sump pan is passenger car style (open/no baffle) then you should upgrade to a pan with the baffle.  A 10-quart and/or rear sump pan is beneficial but not an absolute must in your case. Lastly, if you have the 6-quart F250 rear sump then that can work fine but I'd recommend a few modifications prior to engine install.

my uncle says a high volume oil pump is necessary as well. It's a big day cruiser, so I don't see myself hot rodding this thing.

I feel an HV pump is a wise idea in a jet boat engine and all our jet boat builds utilize them.

...I'm hearing it's better to go with a more modern 4 point engine mount?

If you need one...if your cruiser boat has a sound engine mount system then don't worry about it.

...does anyone know if headers will fit on this thing? or am i limited to logs as this thing has an engine cover in the back like my inboard centurion does, just mounted all the way back.

Headers under an engine cover are not advised unless you have a water jacketed header system . They cost several thousand dollars brand new and I don't think the modest power gains justify the expense

...any recommendations on carb size? not sure if i need 750 or 850 holley. (77 460 with rv cam, and edelbrock intake, and straight up timing gear swap), Any input or tips appreciated!

A Holley 750 cfm shoud be fine in your case; 850 cfm won't hurt.

I can probably walk to your house from mine; feel free to call directly with any further questions.