Radweld? I think we have something similar here in Australia, either K-Seal or Chemweld, not sure which is the equivalent. Both are "temporary" fixes, although Chemweld claims to be a permanent fix despite being mostly silicate that bonds into cracks in heads and gaskets to form a seal (which undoubtedly could cause issues for the poor mechanic trying to perform the permanent fix later).
I've used K-Seal myself, we developed a pin-hole in the radiator on our way to a medical appointment, so I dropped the K-Seal in the radiator, topped up the water and continued ... we then immediately sought a new radiator, had the system flushed and new coolant added. I am not so confident about Radweld though, here's one user's comment on it from a engine-based forum:
That's not the greatest endorsement for the product, but most of the responders acknowledge that Radweld is really only designed as a temporary fix. I guess it's time for the more permanent solution, it's not a pleasant situation but if the new mechanic does a reasonable job the car will run great.
I'd also grab a new radiator and a new thermostat and, while you're there, upper and lower radiator hoses. These are relatively cheap and you might even consider a radiator that performs a little better than standard if you're towing. They'll have the water pump off to do the head replacement anyway, so they can check that out, and they can also have a look at the timing chains (pay particular attention to the tensioners here).