Dont even consider trying to weld any cracks on these blocks.
Been tried many times and the can of worms it opens is simply not a place you want to go.
The crack I see is right at the limits of being repairable with the Lock and stitch inserts.
The crack as to be within the area of the bolt hole (yours is barely) many times these will crack at the register cut, GAME OVER
The whole concept of the insert is that the threads are angled up steeply like the branches on a christmas tree.
As the bolt torque is applied the tension pulls the cracked area back together and also, due to the shape of the threads, there is not any spreading (wedging action).
The real problem with these blocks is that there is a lot of dynamic flexing going on during opperation.
In other words, the blocks is MOOOOOOOOOOOOOOOOOVING.
My gut feeling is that these blocks in mnay cases may have been too GREEN (Not cured well enough) leading to the cracking.
I have seen many cracks at the register fit that actually have spread open. This is due to the casting moving, shrinking and adjusting itself after several duty cycles.
Your block can likely be fixed quite well with the lock and stitch inserts.
A starter kit for the 6.5 is not terribly exspensive. It comes with a several inserts, the drill, tap, lock pins, special locking solution and instructions.
I went a tad farther and made up a spot facer to clean the finished insert up so it is slightly below the original surface (.001"-.002") to make absolutely sure that the caps fit properly.
I have a standard spot facer that is slightly larger than the inserts OD and I turned down an old main bolt to make a "Pilot" for the facer..
Just thread in the pilot, drop the spot facer on the pilot and run it gently with the 1/2" drill motor to clean the surface.
I use a special plate I made that bolts onto the pan rails and has 6 large holes to allow access to the outer main holes.
I then sit a mag drill on the plate, use a pilot to index the original threads of the hole then drill it out with the provided drill. (go 1/4" deeper than the oroginal hole to allow room to seat the insert. ) They dont tell you this in the instructions. Be sure to carefully debur the area of the hole that breaks out of the main web.
Also use a countersink and lightly chamfer the finished hole before you tap it.
Tbe inserts seat better this way.
MGW