Ted:
If my understanding of the situation is correct, you should find no literature on intermetallic formation with fused, or reflowed tin/lead, because it virtually does not happen. The intermetallic happens only with Tin and Copper, not with lead and Copper, and since the Tin/Lead is largely Lead, it may happen at the surface, but essentially stop.
This is why we loved Tin/Lead as a finish for so long...the only problem with it being that it is usually not flat enough....and not contains LEAD....which of course, will pollute the earth...from which we have so recently removed it...
I suspect that you might have some issues with surface oxidation, which should be able to be dealt with by an aggressive flux, but intermetallic should not be an issue.
Rudy Sedlak
RD Chemical Company