which torque specs would you use for heads? ARP head bolts calls for 65ft pounds and merc 75ft pounds.

I always torque the arps to 75 regardless and make sure you seal the threads well with a good thread sealer such as permatex#2.

ARP's recommended torque settings are usually lower because they tell you to use their moly lube which according to them gives about the same amount of bolt stretch with 10 ft-lbs or so less torque. For example, for the ARP head studs I'm using, they recommended 70 ft-lbs with ARP moly lube (for iron heads) and 85 ft-lbs with oil.
They only recommended 65 ft-lbs w/ moly lube for Alum. heads, so I followed AFR's instructions and torqued mine to 75 ft-lbs in 15lb increments.

When I redid the top half of my 525SC, I used new ARP head bolts, the ARP sealant/lube and their torque specs. No problems after 50hrs.

Just like MESA said, use a good sealer like #2 Permatex and use Moly lube with oil under the head bolts and washers. Make sure also you torque in steps as well. After sitting for about 20 minutes or so I usually go back and loosen one bolt at a time and re-torque to its final torque speck. This helps in bolt stretch and tightness. Some do and some don't. Its seems to work for me so I keep doing it.

Good luck.

John