The inserts you will need depends on what size the outer center main bolts are.
Early 6.5 are 12mm and later 506 blocks have 10mm
There are some things that the instructions dont tell you either.
Once the hole is drilled out and the drill hits the bottom of the original hole, drill 1/4" farther down or the insert wont seat flush with the block.
Run the tap "Carefully" until it stops at the bottom of the hole.
DO IT BY HAND WITH TAPPING FLUID (TAPMATIC OR Equivalent)
Back tap out frequently and blow out chips (wear safety glasses too)
You also need to countersink the hole slightly for the insert to seat properly. (Break the edge 1/16 wide with countersink)
I use Tapmatic tapping fluid when tapping the holes.
Dont try to do this with a hand drill either.
It can be done in a mill or large drill press. OR you can do it like I do.
I have a steel plate (1/2" thick) that has relief holes that just sit over the center 6 main holes (Reliefs are 1-1/4")
The plate bolts to the pan rail using flat head allen bolts.
I sit a mag drill on the plate and this allows a good straight drill job.
I then retract the drill, remove the bit, install a center drill as a pilot and then sit the tap in the hole and pilot the tap a few threads by hand using the center drill in the back of the tap as a guide and follow the tap with a little pressure on the mag drill (Motor off)
The tap has a taper pilot in the back, use it.
This works well but takes a little time to do right.
I can do all six holes complete in about an hour and a half.
Once the inserts are installed you must be sure they are absolutely flush with the block surface.
I made up a pilot from a metric bolt that screws into the insert and then touch the inset lightly with a counter bore thats slightly bigger than the OD of the insert.
I just touch it until there is a tiny cut into the iron all around (No more than .002")
This assures that the cap will bolt down perfect.
Also wash the new threaded hole in the block with BrakeKleen and blow dry before applying the loctite product that comes with the inserts.
Be sure the little locking pins are seated below the surface too and then swipe the surface with a good clean FLAT bastard file. **** Dont get wild with the file this is just to make sure there are no burs left********
Once the machining is done the cam bearings must be removed as well as all other oil galley plugs and the block washed completely and all passages flushed with hot sudy water or ???? cleaning agent.
Blow out well and dry.
Done deal.
This may sound like loads of work but is really a very simple job to do.
Now maybe it seems simple to me as I have been in the machinist trade for far too many years.
Any questions??? I will help all I can.
Here are some fairly detailed pix of what I spoke of as far as the tooling and procedures
*** Tell the guys at Lock and Stitch that you need the inserts for the 6.5 and they will sell you the right stuff, just be sure to let them know 10mm or 12mm***
If the outer bolts are the same size as the inner ones you have the 12mm outers.
Missy