Zmodem @ 7 bit xfers

[rmallory@silicon.csci.csusb.edu (Rob Mallory)]

Can anybody help me with this problem?:
I want to get my unix machine running sz to send in 7 bit mode.
<Not just simply escaping the 8'th bit> I'm going through an
X.25 which happens to be 7 bit, and the unix machine doesnt 
"see" it.  Furthermore, the dialup node is 8 bit! 
in effect, the signal is going through 4 computers.

Kermit works fine<it was made for this>, but Proterm has no sliding
window or big packet capability<ugg>, so basicaly Im stuck with a 
horrendous 199<max> cps throughput with 9600baud! 

how can I get:
1) SZ to tell proterm thats its coming over a 7bit line.?
2) Get Kermit (proterm?/Kermit-65?) with sliding windows??
 
-Rob