Well, if you've got compressed air, I highly recommend a Die grinder(preferably a straight body one).
The dremel is nice for finishing work but for the "heavier" porting, the grinder is the ticket.
What you're looking for is removal of ANY hard angles in the combustion chambers and ports.
Basically, any "edge" that'll inhibit air flow.
is the KEY word here.
Even the little edge around the spark plug boss in the combustion chamber.
(great spot for the dremel)
If you check on-line, there are several pics of ported782 heads.
Surely you'll find enough to use as a "guide".
And, you can go as far as YOU decide then.
Porting tools are available on eBay(not the greatest of tools but, you're not machining aluminum heads for a living).
I bought a set of these:
6 Pcs 10mm THK Tungsten Carbide Rotary Aluminum Cut Burr 6mm Shaft 150mm Bcdefl | eBay
Remember: there are specially designed porting bits for ALUMINUM called NON-FERROUS bits.
If you use the "ferrous" bits, they'll clog with material as you grind and become a smooth ball that does nothing.
And after using them, I intend to use this set for finishing:
Best wishes on the porting.
If you were thinking about sending it to a shop, I'll tell you this in advance;
Porting work takes a LONG-LONG time(even for experienced machinists).
That time costs money.
LOTS and LOTS and LOTS of money.
So, if you've got time, why not take a stab at it yourself and see what you can do?
VERY IMPORTANT TO KEEP IN MIND:
When you machine the combustion chambers and ports,
BE SURE TO CHECK THE VOLUME OF EACH AND MATCH THEM TO ONE ANOTHER.
Keep us all updated.