Well, again, you could check out PAECO; last time I looked they rebuilt
engines in 4 grades, 3 performance levels from street to all out
racing, and a fourth built with racing strength but street performance
for ultimate reliability, price is not cheap but probably cheaper than
factory, I liked their work and they've been in the small engine/import
performance biz since forever, way before the Japanese invasion (or you
could get a short block or heads from them); or look around for other
volume engine rebuilders at mass-market prices, they're presumably
standardized as to process; or get a used one and even if it should die
in a few years, you've saved enough to get another used one and still
be ahead of the game; or go with your mechanic, as you said there are a
lot meticulous things to be done but most of it is just a matter of
being meticulous.

Boring story: my first real experience with mechanicing was sort of a
total immersion way back when, when what began as a simple drivetrain
swap in a Corvair turned into a drivetrain swap with swapping heads and
ended up as an entire engine rebuild except for the heads, me with
minimal mechanical experience and not much cash, done at one of the $2
an hour public rent-a-garage-bay-and-borrow-tools places they had then.
(This was what happened after I bought the previously mentioned Corvair
with the brand new rebuilt heads which had immediately thrown a rod,
and wanted to merge it with my 100,000 mile old crapped out but running
Corvair which had just been rearended by a school bus) Took 2 weeks,
about 8 hrs a day, I played hooky from college. I dragged the
crankshaft to a machine shop to do whatever it was they needed to do
(grind it true?) in my innocence I didn't bother with reboring the
crankcase or the cylinders, just honed them, didn't use the plastigage
to determine whether the bearing clearances were correct, just miked
them and got the right size bearings, same for the rings, didn't check
oil pump gear tolerance either, didn't check ring end gap, managed to
botch the positioning of the ring gap so that the edge of it caught in
the notch in the bottom of the cylinder barrel that was there to clear
the con rods, but I was hugely careful to clean out all dirt, grit,
metal, etc., carefully use cam prelube etc., since all that wasn't
rocket science, just obvious good practice. Anyway, after I got it
together I discovered I had to rebuild the carbs too, but after that it
ran like a bear and had no problems until it got stolen (most likely by
one of the guys hanging around the shop who "helped" me). Point being,
I guess, that for most of this stuff it's not a matter of being rocket
science perfect, even if you're a little outside the specified
tolerance it'll be OK, it's a matter of avoiding the one big goofup
that'll destroy the engine. If a hamhanded (still) and not very
knowledgable (then) guy like me could rebuild an engine successfully,
then a mechanic who was willing to take the time to be careful ought to
be able to.

I believe that at this point, I've argued both for and against all
points of view... ?