Your 351 is equiped with the ProTec ignition system. The typical distributor is replaced with a position sensor and timing is done electronically. The black boxes on the aft end are coil packs. If the engie runs then that's good but, the system does have issues. Many have had to resort to removing it and replacing it with a distributor and traditional coil. The good is it's an easy swap and kits are even available. 

Regarding a tune up, about the only thing you can do is put in a new set of plugs. 

I caution you on oil. Your 351 is an old school flat tappet so it needs old school oil with ZDDP. The ZDDP has been removed in many modern oils. 

You need to figure out if you have the pro tec still working.

It may not start at all if even if the motor is good.

I have the same hours and mine still works but its going to go eventually.

Motor wise pull your plugs and look at them. They always have a story.

You might handcrank the motor to make sure its spinning free before you do all this work.

Make sure you have good non ethanol gas in it.

Mine runs great and the decal and manual clearly state not to run ethanol

Prime the carb with gas  and let her rip

I hope you are lucky and it shut down your engine.  I have been in a boat when the hoses cooked and collapsed.  The power falls off quickly till it almost kills the engine and it starts stuttering badly.  It sounds like the engine has burned up and died plus you smell the burning exhaust hose and it smells terrible.

Both of the boats mentioned were just fine, no damage other than new exhaust hoses, I hope you are that lucky.

As soon as you look into the hose you will know, if the interior is closed off you are lucky.

Understand that all Mobile 1 oils do not have the same levels of ZDDP. Mike is correct that the 15W50 does.

Nautiquehunter wrote: If you choose Mobil 1 the 15w50 is the only weight recommended by Mobil for non DI marine engines.

Lots of other oils out there too. A site search will turn up more than you need to know and plenty of opinions. 

To late to delete. Sorry. 

Thanks Ken. Yes, I'll delete the post to hopefully reduce any confusion.

Closer to 5 with a filter. Add 4, run engine and check the level. 

Yes, the marine alternator is ignition protected. 

More amps are possible but, depending on the load,  wiring and circuit breakers may need upgrading. 

You could look at one of the alternators in the link below

It's a replacement for what's in your boat whether it's a Mando or a Motorola that you have now

It may not say that it's for a PCM in the title, but if you read far enough in the applications list, it gets mentioned.

It'll bolt right in and wire up easily.

You may have a jumper on the back of yours that's not shown in the link, but you can swap it onto the new one or make one pretty easily.

I'd talk to DB electrical and tell them what you have and they should be able to confirm that's what you need

A picture of yours  from the back and front would be good for comparison purposes.

Unless you're planning on powering all kinds of extra stuff, no more amperage is really needed. 

http://www.dbelectrical.com/products/mercruiser-omc-volvo-marine-mando-alternator-293-18-amn0002.html" rel="nofollow - link

Here's a picture of a Mando that came from a PCM 351 and you can see the jumper bar that goes from the output terminal (with the cutoff orange wire) to the "s" terminal that would have to be swapped over.

The red wire on the one in the link isn't used in the PCM application due to the jumper bar being used instead. The bar provides output voltage to the sensing terminal for the voltage regulator