While I'd certainly prefer that nobody bring a torch over to an aluminum head, the repair that they plan to do is unlikely to cause any long term ill effects to the head, provided that they only heat it in a localized area to apply the filler material.

Before proceeding, please weigh the cost of the head, and the repair, against another head that is in better condition.

I do understand the lack of immediate availablilty of these heads, so, clearly, that will weigh on your decision.