Could be either, or, not related at all. Not trying to cloud the issue, but lack of correct lifter preload(bottoming out) and no seat pressure, might manifest itself as an intermittent backfire, but it would probably also require a "change" in stociometric air/fuel outside of the normal.
Does this "intermittent" backfire occur anywhere, or time in particular ? ie; on decel ?
How long/far have you driven this other vehicle ? Surely, lack of correct lifter preload(seat pressure), will cause a prematurely burnt valve. Exhaust Valves especially, disperse their absorbed heat, through contact and pressure to the head.
Think of if you lightly touched a hot iron with your finger, now, "press it hard" to the hot iron for the same time. See what I mean, more "heat transfer" and a really "****ed up fingy" !
Also, There is a range on either end of stociometric, where air/fuel burns "fast and erratic" either rich or lean. Hence, timing setup done one day, works great, then the barometer drops and presto ! CRAP ! All because most carbs utilize an emulsion tube/fuel jet/air metering system, sensitive to air pressure, hence, they make tools called "timing lights" for "suggested", and more "forgiving" timing specs.
Power timing works great too, but really, when done with the engine in gear like it's "apposta", all we're doing is eliminating the Timing chain slop by loading the engine.
I always P/time WITH a timing light, and the engine in gear. Why not use all the tools available ?
Long story short, need more info on your backfire ! May, or, Maynot, be related to tip hts.
