milling heads for comp ratio increase

If you have 675 heads, then count on around 68 cc's. Not 60 cc's; the NHRA minimum might be that, but the general factory chamber will be around 68 cc's.

Just know that the Mopar 'factroy' CR's are general optimistic by about 3/4 of a point over standard production. Your true stock CR is really around 8:1.

With your open chambers, the numbers given earlier about losing 1 cc for every .005 or .006 " shaved off is correct.

For street use, having better low end torque will be very much worth having; that is the point made by BigBlockMopar. Better torquer just driving around and better fuel economy. Getting the higher CR will be worth it. But, if the costs are too high for your budget, then going with the thin head gasket is most all you can do. The common thin gasket over here is the Mr Gasket 1121G. BTW, if you put in flat valves, you are going to lose about 2 cc's per chamber so that is not a big change in chamber size.

Does shaving the heads and intake to match cost a lot less? If it did, I would go that way. IMHO there is nothing 100% sacred about doing it one way or another. The shaving of the head on the intake side by 95% of what is taken off the bottom is just a way to not have to mill the intakes. If you don't mill the intake side of the head and then changed intakes later, then the new intake would have to be milled also. So that is why guys mill the intake side of the heads: to maintain easy future intake interchanging. But if you are going to keep the intake, then do it the easy, cheap way and move forward.

You mentioned Edelbrock heads. It would be an imporvement in CR over 675 heads, but the issue will be the valve size requiring the block to be notched. I tink you'll have the same problem with the Indy heads an their 62 cc chambers.

Have you looked into cams yet? There are some low duration high lift cams that would be worth your while in your use.

There is probably a combination of Silvolite Holden 253 pistons and long Eagle rods that can work with some machining, but I bet that would cost much more $$ so is probably not a good idea at all for your budget.

I wish we still had "ute's" over here; we had Ford Rancheors and Cheny El Camino's but they are gone from the market.