rats!
I saw a pair of "ram horns" at a swap meet today--10 bucks for the pair,with new studs already installed!--If I had known you needed them I'd have bought them and sold them to you for 20!...too late now though..
But as far as drilling and tapping goes,the only way to learn how is by doing!--use a small bit like a 3/16 at first after center punching it,then use a 5/16 drill--(the correct size for tapping a 3/8 hole!)...I'd practice on some old parts first before attempting to do the manifold(s)!..it IS a bit tricky!--getting to know the limits of how much torque the tap will take before it snaps off in the hole is the hardest part!.
.Use oil or kerosene on the tap!..you need to screw the tap in a turn or two,then back out--repeat until its all the way thru..dont force it too hard!--if you feel the tap twisting,its about to snap,back it out and clean the chips out and try again..You can buy a "T" handle for the taps,or special sockets so you can use a rachet--I use a small adjustible wrench most of the time--the "t' handle wont fit in most places..when tapping a "blind" hole like your thermostat bolt,be careful not to "bottom" the tap in the hole-it WILL snap off,and its a bitch to get a broken tap out that "hit bottom"--just like a bolt,but worse!...
I'd buy a couple of taps--the 3/8 ones get a workout on chevy's,since its the most common bolt size on them.(and its likely the first one wont last long,if you have little or no experience using them!--you havent lived until you have to get a broken tap out of the hole your tapping--they make tap extractors(costly and hard to get)--or a punch and hammer can shatter it and hopefully not the part your trying to save--my favorite way is to use the cutting torch!-(yeah,I break em despite all my "experience"too!)-taps melt faster than mild steel or cast iron,and flare up like sparklers on the 4th of july,I think the torch is fastest and best for that job..a light pull of the trigger and POOF,no more tap...
The drill bits are up to you--any "high speed steel" bits will work,the "titanium" yellow ones last much longer and will drill harder steel without dulling so fast(kind of important on exhaust studs,they get hard after many years of being heated up and cooled off..)..beware of China drills that are barely capable of drilling wood!.( buy name brands like Vermont American,etc)...as for drilling them out,a hand drill works ok,but takes a good "eye" to drill it straight...
A drill press is challenging too,as you need to use wood blocks to align the manifold with the bit--one with a tilting table is a blessing!(mine ain't,and its a benchtop model--too short to get most manifolds under it

)..its a job that takes practice to get right--I did hundreds of broken stud removal/retapping at the parts stores machine shop I worked at--got pretty good at it after awhile,but I still have a few that I pooched beyond repair!..even with lots of practice,you still break a few taps once in a while...
I know a guy who worked at Midas Muffler shops for many years--he can use the torch to remove the stud,he just heats it up and blows it right thru!--then he runs a tap through the hole and its DONE--he does not even take the manifold off in many cases!..and he is real good at getting them out if a little is left sticking out too--a lot better at it than I am!...
