I had thought conceptually about this approach and like yourself, could have probably got a string buffer to work.

Ultimately I took what I think was the easiest course of action and that used in most of the posts I found here. Instead of using DEBUGIN I used HSERIN on the input side and the LCDOUT on the output side at 2400 baud with a and 4 pin data bus to the module. The code illustrated in several posts just envolved a character for character transfer with the PIC just cycling through read, biding the time between characters. At 2400 this seemed to work fine.

This solution meant changing my circuit board so that the hardware RX pin was used for input. On the 16F628A this meant I could not use all 8 PortB pins for output to the module. I disconnected the wires from B0-B3 to the module and just used B4-B7. The whole board was designed for an assembler code by one Tom Coonan which is available on the WEB. I just couldn't get it ported over to the 16F628A and have it work right. After 3 weeks of messing with it I opted to use the PIC Basic solution.

In any case, I have the "Backpack" working again and at 2400 I have tested it with another PIC as the sender and aslo Hyperterminal on a PC. It works fine now!