Milling the Heads How much?

The heads are 79 318 heads, I have done some mild porting and went with a bigger valves. I have not done a compression test which is a must do to really get a better direction to go. I am toying around with ways to make what I have a little better. Believe it or not the combo I have is only putting out 200 hp and about 275 ft lb torque. I want to wring what I can out of this combination. I am on a very thin budget, almost transparent and can only afford certain things and really don't have the cash to do major things. So I was just seeing if there is anything I can do with what I have and get a little more out of it. Before the dizzy fiasco the car was dead reliable I could drive it any where and got about 20 mpg out of the motor. I am running a 10 1/2 inch clutch with a kevlar disc and 3000 LBS pressure plate. The weak link is the 7 1/4 axle with 2:76 gears. I have a 8 3/4 out of A 100 that I would love use as a trade for a 8 3/4 SBP rearend with possible 3:23 gears. So any suggestions......maybe a junkyard turbo??????