Oh rollocks, not an area I know well, but not, luckily, so far out in the wilds that this is a major problem. There's hope yet!
Question is, where are the pups going to be born and where will mum stay with them? He can't take her onto the street whilst she's whelping or nursing puppies.
I think that's what you'll have to establish first and take it from there. Also please pm Kaye, the owner of Lurcherlink now - you and she may not be able to do anything right now but Kaye will have FAR less chance still of being able to help when the pups arrive or if there is a problem if she has no prior warning of the situation.
The owner needs to be put in no doubt that rescue will NOT just take in his bitch and care for her whilst her pups are being born and then return her to him. Rescue VERY rarely offers any form of temporary care for an owner and even if it does it's generally under special circumstances and/or for someone they know. If he wants rescue's help with the pups he will have to sign them over to rescue and if he wants help with the bitch in terms of care whilst delivering and whilst she is nursing her pups he will HAVE to sign her over too. There is NO WAY that rescue will take in the bitch and then hand her back, unspayed and ready to get pregnant again when she's raised the pups.
I'd ask you too to ask him what he will do if his bitch needs a caesarean section or medical care when she starts to deliver. (This is one of the reasons why I suggested offering him money to get the dog into immediate safety). Sorry, I'm not suggesting that he doesn't care for her but the potential for a disaster for the bitch and her pups appears to be huge here and he needs that spelling out. Bottom line from my POV is sod that he cares for the dog, this isn't about HIM, it's about what's best for HER and being a big person, putting HER welfare above his own desire not to lose her because from what little I understand he could lose her for good anyway.
I hope I'm wrong and that he's thought all this through and got the solutions already lined up, but these questions need asking just in case he hasn't.