As Sara3 suggests, get to the court early and try to speak to a representative of the probation service (or get your solicitor or barrister to do so). If you're lucky (and you'll need to be!) the court MIGHT agree to delay sentencing until after another attempt at getting a pre-sentencing report. However it's far more likely that the court will simply sentence you there and then.
Guideline sentences for Section 47 (ABH) are on page 17 of this document:
http://www.sentencing...inst-the%20person.pdf
(See page 15 if it was actually Section 20, GBH, which you were charged with).
However those sentences refer to a first-time offender convicted after a trial. Your previous conviction will push the sentencing range higher but the sentence will be reduced if you pleaded guilty. Since we don't know whether the offence was pre-meditated, whether it involved the use of a weapon, or the extent of the victim's injuries, I'm not going to hazard a guess at a specific sentence but custody is certainly a distinct possibility.
Chris