As for the mic and PTT, you will need to make an adapter from the 6 pin modular to your Heil connections (1/8" mono for mic, 1/4" mono for PTT). You can go to http://homepage.ntlworld.com/rg4wpw/date.html#yaesu
and look up the pin out in the 8800.
The 6 pin modular on the 8800 is the same as a RJ-12. It is an RJ-11 with all 6 slots active. It may be a little hard to find. Most telephone cords are RJ-11, 4 pin jacks (6 slots, only 4 active). If you keep it short, you shouldn't have to worry about RF getting into the adapter.
As for the headphone, run it to the ext speaker jack (1/8" mono). You will need to set Menu 39 "SPCONT" properly. There are 4 settings:
EXT: The audio is routed to external speaker (internal speaker is off).
OFF: The audio is not routed (internal and external speakers are both off).
INT.EXT: The audio is routed to both the internal and external speakers.
INT: The audio is routed to the internal speaker only (external speaker is off).
I would suggest EXT for your "working" side, and INT for your monitoring side. Or EXT for both. You have to set it for each side.