The C=64 had 64KB of RAM. The 1541 disk could store 170KB on a side. Since the serial link between the two was the bottleneck, and both the computer and disk drive had the same 6502 CPU, it seems like the optimal performance would be achieved by having the computer send the document to the disk drive, and having the disk drive do all the actual work.

Implementing a spell-checker this way would probably take many more months of work. :-)