I'd recommend doing it yourself.

Now-a-days, that is about the only practical way to overhaul an old model
engine.

The more you learn about your engine the more you will be in tune with it's
perforance (or lack).

Parts will be your biggest expense, since Volvo parts have always been very
very expensive. There are a couple 3rd party sources for major parts.
http://www.adiesel.com/volvopenta.php

Your biggest expense will be the cylinder sleeves.. If they are worn beyond
the limits, they should be replaced rather than going oversize. (my opinion
FWIW) That way you can usually still use your old pistons and standard size
rings. If you were able to bore the cylinders, you would have to purchase
oversize pistons and rings.
(come to think of it, I'm not sure that the MD11C has removable sleeve
assembles, like the MD2B.)

Additionally, replacing the sleeves removes one of the three parts that are
subject to sal****er corrosion (cylinder, head and manifold).

When you rebuild the heads (have a shop do the valves for you) have them dip
tanked or sandblasted and magnaflux inspected for cracks or (near) rust
through.. I've never known of a Volvo MD head to rust through but cracks are
possible around the valve seats.

Watch for a good price on an exhaust manifold since they are usually the
first to rust out at about 20 years in SW service. Since the manifold is
easy to change later, I wouldn't bother replacing it now unless it shows
diffinate signs of rust thru. Don't be alarmed if the 'freeze' plugs are
corroded since these can be pryed out and replaced.

Almost everything tool your going to need are basic combination wrenches and
sockets (metric), about the only additional tool you might need is a torque
wench. This you may borrow from a friend or rent one at the time you get
into assembling the rod bearings and head/manifold bolts.

The flywheel will be the most difficult and you will need a large socket for
the nut and a large puller (again, rent) to pop it off the shaft.

If you thing the transmition needs work, you may want to send it out. The MS
type is more complex and requires special tools for assembly, while the RB
could be done by a owner without special tools.

So, get out your Volvo Workshop Manual and read through it, I think you will
be encouraged. Not a big deal.


--
My opinion and experience. FWIW

Steve
s/v Good Intentions