32 is the limit that is documented, but there is a way around this. (I will warn you it is not perfect, and not supported by Nortel, but it does work)
Take Digital set #30 (in your line of 48) and set the FDN and HUNT to an ACD DN. You will need to configure the ACD in advance; set MAXP to 1, and MWC to YES. Then set NCFW to the DN on set #31 in your line.
Once you have make set #30 FDN and HUNT to the ACD, go back and set MWC on the ACD to NO.
This will break the chain and essentially restart it. I once had 112 trunks working this way, not by choice, but it will work.
One item of reference is that we did have a few calls that would kick out to the receptionist during high call volume, but with only 48, you should be OK.
***** Again, this is not a preferred method, but if your customer must have 48, this is a way to give them what they want.
Hope this helps,
Scott M.