Front brakes/struts are a thing to ask as some like to see upgraded disks like stanza or sunny etc.
Fuel lines, some allow copper some don't (I found out the hard way mine didn't like copper, even though he approved 2 conversions before mine with copper lines)
If you using harnesses what requirments etc for mounting.
Transmission mount (I had to have mine bolt through the chassis rail (with crush tubing inside).
Is a tailshaft loop required? Find out if he wants one of those installed.
Ask about if he has any preferences as to where he will allow you to mount to fuel pump and surge that way you can bounce ideas and designs off him.

Thats all I can think of off the top of my head, but dattodude has probably given you all those things to ask.
Cheers
Damian