yes, I think so, I would suggest you look into it and discuss it with your social worker. Basically, a special guardianship is cheaper for social services, they leave you with temporary parental rights ( which can be revoked at any time) and no support.
Unless the system is different in your part of the country, special guardianship is the worst of all worlds. It isn't adoption, so you get no security or permanence, and it isn't fostering , so you get know financial allowance or support.
Ask your social worker about it, it may well be that there are so many barriers put up to prevent people choosing kinship fostering that its just easier to go along with being a special guardian.
However, even if you ask about it, and they say no, at least it shows you are aware. I have known reluctant special guardians to receive a one of payment of thousands of pounds, on accepting the situation, and I'm sure it wouldn't have happened if they hadn't have worried social services by showing some reluctance.
I don't want to raise your hopes, or to complicate the situation, just want you to get the best arrangement you can. A child is very expensive, and not only that, but this one is likely to be complicated, having already been inadequately nurtured, he will be damaged.
he is very lucky to have you to step in and be prepared to love him and make sacrifices for him. I'm sure you will do a great job. but please, at least ask about kinship fostering, it might not be available, but even if not, then some of the benefits of it might be made available to you, support groups, training, etc.