You can power the timing light from the ignition coil lead.  This is what I
have done for years, it may be risky or something but I have had no
problem.  The positive terminal on my coil is the lower one and I use a
random bolt on the engine for the ground.

If your remote starter is the type with two aligator clip connectors on it
then you can connect it directly to the starter.  You should be able
to connect to the primary lead (large cable running to bolted connection on
starter solenoid switch) and to the upper of the two spade connections on
the starter solenoid switch.  I think that is the setup on my van.  If you
confirm that your van is in neutral and block it etc. then you can test the
button while you are under the van in order to figure it out (don't run over
yourself).  Most remote starter switches will have enough cable on them to
enable you to keep the switch on the back bumper or thereabouts.

Jonathan Poole
'82 ac westy