Rock and hard place come to mind! 😮
If you buy a replacement head (cost???) then you get the car up and running in a saleable condition. If you then provide the original head to the new owner to do with as they think fit (get it repaired and fitted to the car for originality or polish it and use it as a garage ornament or just plain junk it) then i don't see the value being reduced.
Also here in the UK, we're not quite as focussed on "all matching numbers" as it seems our stateside cousins are. With this in mind, in the UK it wouldn't make any difference unless someone really wanted originality and even then, there's no way the car could be truly original at 60+ years old. Tyres, brake parts, the list is long of parts that wear out and besides, after a full restoration, it would be unlikely the engine would be original to most 60 year old UK cars.
What are the costs of having the original head repaired with guaranteed work and how does that compare to the cost of the replacement head? If those costs are similar then the answer is fairly simple, get the existing head repaired and fitted, this would satisfy the "matching numbers guys" and not really cost more. I can't really comment on the value decrease for the reasons above, however i do know from having watched things like Counts Kustoms and similar that in the USA a premium is usually applied to the price when selling a matching numbers car and is normally paid happily by the buyer for that provenance.
Not much fact-based arguments above, more like based on what i feel is a common-sense approach to your dilemma but hopefully you can take something from it and make a decision.