I ended up using ARP studs, they have an allen head so I won't have to double nut to put them in. I also used ARP nuts and washers.
It feels very much smoother when you torque the intake manifold down. Very expensive though.
For my PI intake I used:
Studs to mount PI intake (qty 8 ) 3.5”, ARP AJ350001B
Studs to mount PI intake (qty 2), 2.5”, ARP AJ2-500-1B
Flat washers to mount PI intake (qty 10) 3/8 ID, 5/8 OD, .120 thick and hardened ARP-200-8504
Nuts to mount PI intake (qty 10) 3/8-24 ARP 200-8604, it's listed as a rod nut and has a nice shoulder.
Sometimes it's cheaper to buy a 10 pack, but I found it cheaper to buy 10 individual nuts/washers.
For the thermostat housing I used a Spectre Performance 42513.
This is a carb stud kit so you get 4, what's nice is they have a narrowed down tip so you can start the nut easier and it can't fall off while you are putting it on.
It also has a hex on the end of the stud for turning in if needed. Nice for only $5 and I'll put the other two on my other car.
http://www.summitracing.com/parts/SPE-42513/I also bought an ARP distributor hold down stud kit ARP 150-1702.
This also has a necked down tip so you can start the nut easier.