345 in Scout 800? And carb questions

[MikeIIDC@domain.elided]

Well, now that I have taked about his, I wanted to get one more round of
input on my 345 into an 800 question.
I was under the understanding that the 345 would go into the 800 that
was set up for a V8 without too much difficulty.  Tark the other day
suggested that I may have to add a couplke inches of body lift to do
this, as the 345 is taller.  Anyone done this?  I thought that the
problems with putting a V8 vs. a 4 cylinder had to do with the radiator
mounting configuration and room in the front.  Is clearance height of
the hood going to be an issue as well?
I drove the Scout home from the exhaust shop, and it was much quieter
than before, but has a SERIOUS backfire problem.  It was only about .8
mile home, but I fear I may have blown one of the mufflers completely
out.  Since I've had it I tuned it up, rechecked the points, and
rechecked the timing.  I believed originally that the carb needed
rebuilt, but put the carb off of my '68 T'all on it-this carb was
recently rebuilt and was working fine when the '68 was on the road, but
has sat about six months since the accident-and it still acts the
same-drinks gas very quickly, backfires like a cannon, and, though it
will pick up speed now, which it wouldn't before, the guy at the muffler
shop said he was hearing a "knock."  I am now kind of fearing the
worst.  If it is knocking, I know that this is sometimes a main
bearing-what else are possibilities?  Also, I know that people fear and
dread engines with "knocks" in them, but also know that some people
claim to have driven for years/thousands of miles with a knock and never
had a problem.  Since my old '73 was backfiring with low oil (sticky
lifter?), I thought I would "overfill" this one slightly and see if it
helps-that is what helped the '73.  It seems that the backfire is always
coming from the right cylinder bank.  Could this be another "sticky
lifter" problem-just more extreme?  Stuck valve?  Worn cam not pushing
the pushrods enough?  The odometer reads 07000 or something, and though
the thing is rough, the engine bay is so clean that I had assumed this
was only 107000.  In this case, I would not necessarily expect it to be
something that big unless it was really abused.
Anyway, I am looking for any ideas as to the origin of this backfire, as
well as any suggestions on the 345 swap.  I need to know if the body
lift will buy enough room in the right places, and how much lift it
might take.

Thanks!

Michael