stage II heads on a stock block

Yes you can. You will only be able to use 8 of the 14 head bolt holes in the heads, will need stage II intake (off center) and exhaust manifolds and a stage II cam. In a Regal you will have clearance issues with the a/c box. Oh, you might also have clearance issues with the valves hitting the edges of the cylinders on a 3.8 bore motor, depending on the valve size, but I've read that this can be dealt with by valve choice and notching the cylinders.

Should you - here's where everyone is going to chime in and say that stock-style aftermarket heads can flow enough to max out the stock block so why bother. Hey, it's your choice, to do for your reasons.
Stage 2 heads

I think that's is overkill the 109 engine is better use the champion alum is less expensive. Intake,headers,scorpions rockers and dont forget the size of this valves

You will need to have a bottom end capable of 7500+rpm to take advantage of the s2 head design. Not worth it in a stock block. The availalble aftermarket heads will do much better on a stock block.