What would a 1946 Snark with A-bomb warhead look like?
The engine technology of 1946 means that the Snark will be shorter ranged and slower than the OTL version. Probably will also be able to carry a smaller warload, too. Maybe underwing drop tanks to add fuel, and to alleviate speed problem, the engine would then be run at full power for the entire flight? Two engines instead of one, maybe? Afterburner for the final dash across enemy air defences? The navigation system is the less accurate the farther away it is launched though, so together with the anticipated shorter range, the missiles would have to be forward-based. Which would probably mean they would be camouflaged? OD/Neutral Grey or overall OD maybe, with water-soluble white pattern sprayed on during winters in Europe and Alaska (the most likely launch sites)? Would they also have the AB-C style letter codes around the fuselage star-and-bars? Nose art?
Also, when deployed earlier the Snark would be even more unreliable than in OTL, so several missiles would have to be assigned for each target (which was/is done even with the more reliable means of delivery). Assume each is launched from a different site to ensure survivability. Say, a Wing consisting of five squadrons of five missiles each, each squadron firing its missiles at the Wing's five target cities. Though, its survivability in 1946 would be orders of magnitude greater than when it was finally deployed in OTL, due to supersonic interceptors and surface-to-air missiles being nonexistent.
However, the real problem is the availability and miniaturisation of nuclear
devices*. The OTL Snark could carry a 6 000 pound
physics package*, and we already assumed that the 1946 Snark would be able to carry less. Problem is, in 1946 the only devices available to the US were similar to those
initiated* over Japan, Mark 2 (Little Boy) and Mark 3 (Fat Man) bombs, each weighing some 10 000 pounds, and of these, less than ten could be put together in 1946 due to bottlenecks in enrichment plants. Production of fissile material and initiators sped up starting from 1947, but even so, smaller devices such as the 2400 to 3200 pound Mark 5 and the 1700 pound Mark 7 were not available until 1952. But let's assume for argument's sake that if there was a need, then a package fitting the Snark could be procured in time (without the Snark and with only a few warheads available, there was also no real need for anything smaller that could fit on a B-29 or B-36) and in sufficient numbers.
*) Gotta love the hypocritical terminology regarding nuclear weapons. Yes, I know that initiation is the technically correct term as detonation refers to supersonic combustion and not the initiation of a chain reaction, but still.