I have had reply from Marc Robinson (a really good guy) - the IC 735 can be connected to the Pactor III.
I will send you his reply via a PM - he has all the knowledge and components to set you up for Winlink and can advise how to do the mods for Sailmail if your IC 735 does not have the appropriate frequencies.
As far as the Tuner is concerned the standard Icom
tuners for the 735 are the AH 2 and the AT 150 - these are no longer made - they were replaced by the AH 4 and the AH 180.
Here is a review of the radio :-Icom IC