Dont know much about old Holden straight sixes but when we were younger we were always playing with 4cyl motors/heads, 1600 or 1800cc head on a 2000cc motor ect.
Could try 149, 161, 173, 186 head on it, use a die grinder to smooth it out a little or go get it shaved but I don't think its going make much of a difference.
I wouldn't really bother with a cam on a 202, but then again its your choice.
You already have a 2 1/2" exhaust, if you haven't already got extractors I'd be looking in to that next.
Seriously though if I was you and if I had the room I would buy a 2nd car to stick in a shed and work on it over time to make it exactly how I want it for when I get off my P's.
Also if room is a problem you could probably just buy a 304/308 to work on over time, put a few $1000 in to it over the time you will be on your P's and drop that in when its time.
Although you know probably already know VK's dont have much resale, mild 6 or not. You could spend $5k on that motor and probably only get half of it back when the car is sold. Pretty sure you wont be keeping it forever especially as a 6.
Don't get me wrong though, nothing wrong with 6's, Ive had a LJ coupe, HR Special, VN Calais and now a VT and they have all been 6's. Loved the old red motors cos they are great to work on your self, loved the balls on my VN, took me ages to get used to driving it without spinning the wheels. VT is nice doesnt have the balls the VN does down low but its perfect for long drives and over taking.
If you have money to burn and/or will keep that car with the motor thats already in it forever then I would be looking at a rebuild and adding parts that you want at the same time, if you would be paying someone every time you take the car to them to get something done labour will be worth more than they parts you wanted.
Or.. sell that and buy a VN S1 V6, they have the balls you are looking for that you probably couldn't get out of the 202 unless you have a bottomless pocket.