The latest printer drivers generate unbound PCLETTO fonts. And, they only download the characters that are being used in the document being printed.
Most drivers only use a subset of the available character cells in a single-byte character set. And, when they run out of character cells, they redundantly download the same characters and assign them to the next temporary download font character cell. So, in a 100 page file - you might have capital "A" 20 times.
And, the fonts are incrementally downloaded in batchs of cells and not in one continguous font.
So, the big question is "Why do you need to convert a PCLETTO font that is generated from a TrueType font back into a Truetype font?". The only reasons I can think of is to create a PCL5e/PCL XL interpreter or to capture a TrueType font from a system that you don't have access to? There are already 10+ commercial quality PCL intepreters on the market and another 300+ interpreters looking for this type of conversion to make them compatible with PCL5e/PCL XL printer driver-generated files.
In my opinion this is definately a "Buy", rather than "Build" solution. You're looking at 300+ hrs. of intermediate to senior software engineering time before you arrive at a viable solution. And, I that's highly dependent on the relevancy and size of your suite of PCL5e/6 test files.
We've been converting PCLETTO to TTF for many years. And, HP's new Universal Printer Drivers in Vista, Win7 and beyond generate these fonts in new ways that have caused us to adapt our product to them. It's a moving target.