If you go with the .030" over bore, or even the .060" overbore, it will not fix the low RPM bog that you have. You will get around 0.2 of a bump in SCR/DCR with .060" overbore.
IMHO, going to a larger bore will do one thing for you: You will start with good straight bores, with the proper piston-to-bore clearance, and a good ring seal will result. A good ring seal is one of the 2 fundamentals to good performance; the other being goo valve seal. I don't ever do an engine anymore without a re-bore; I've been down the road in my poor college days with reqowkring an engine with poor bores.
Balance is probably gonna be on the order of $250-300 complete. You can save some $$ by:
- Setting up a way to correctly weigh both small and big end weights of the rods and doing the rod balance yourself. That is a tedious process but it the larger part of a full balance job.
- Weigh the pistons, rings, and ring locks your self... easy.
- Take the weights that you have from the above steps and give those to the machinist to compute a bobweight and just balance the crank only. (Or, compute the bobweight yourself and give that to the machinist for balancing the crank; that is what I do; it is just some math.)
- If you can give the bobweight or bobweight info the machinist, that should cut the cost by more than half. I recently paid $95 for a crank balance this way. (But our local shop costs are lower than standard.)
A smaller cam is not going to lower you DCR, it is going to raise it... which is where you want to go. The general cam profile of the present cam is decently steep to help DCR, but the duration is just too long, and the resulting intake closing angle is just too late.
Looking at cam options, let's try the smaller Lunati VooDoo hydraulic cam with a 253 duration in stalled at an ICL of 106. With the 302 heads unmilled, the block not decked at all, 1121G head gasket, and the 526 Silvolite pistons (no eyebrows), you end up at 8.6/7.5 DCR with about the same lift that you have now. Change to the smallest Crane hydraulic (the H-248-2) at an ICL of 106, then you are at SCR/DCR of 8.6/7.6, with a lot less lift than you have, so your RPM range is going to shift 1000 RPM or more downward.
That 7.5/7.6 DCR range is about as high as you are gonna get with any sort of cam and the stockish cast pistons and thinnest head gasket and 64 cc chambers. Some head milling to get to a 60 cc chamber would get you up to the 7.8 DCR range with that smallest VooDoo cam (to maintain decent lift) and you are getting into pretty good DCR territory now. Low end torque will be pretty darned good now, as in easy to spin the tires with that 3.23 rear gear.
I think you will be pretty happy in the upper 7's DCR range; I'll guess that you are looking for a 'spirited, spunky' car that still has good driveability. 7.8 DCR will do that, and 7.5 DCR will be a whole lot better than where you are now. Keep an eye on not being too aggressive on the ignition timing. What fuel octane do you have up there?
