I would suggest you write to the boss confirming the new arrangements by setting them out in your email as you understand them and then suggest that it might be prudent to put the changes into a new formalised contract. That way, even if no formal contract is forthcoming there will be a record of the changes and unless the boss denies them promptly then your email will at least provide prima face evidence confirming the details of your promotion. Your email, coupled with financial evidence of your newly increased pay ought to convince a court or tribunal that the promotion was in fact real even if never formalised with a contract, should it become an issue in the future.
The email might be worded along the lines of:
" I note that the terms of my recent promotion have not yet been formalised in a new contract, and in the meantime just to ensure the new terms and your expectations I confirm the new arrangements as follows: (set out the new pay, obligations, etc as per what you were previously advised."
This should prompt the boss to arrange a formal contract but if not, at least you will have evidence of what the new arrangement was should it later be relevant to legal action or working out your entitlements to superannuation, redundancy, etc.
I trust the above assists.
Good luck and please rate my answer.