No, you can't arc weld them. You need a TIG welder for the REAR to fix the cracks (or front/rear for the Series 1).
The front manifold is Cast Iron, so you need NICKEL rod to build up the 'necks' and you better be a very good welder to not have any voids. Criss-cross side by side beads, alternating directions each 'layer'. Then grind out to match the rears.
My coating has held up perfectly (although I did recoat them last winter when they were off the car, it was only to get the areas I couldn't hit while they were installed for the original coating test).
A couple others have used the same coating since me with success. To this day, mine look as good as the day I applied the coating. You CAN brush it on but I suggest you go to your local paint store for the little 'touchup' sprayer. Glass tube with a propellant cartridge. Works like a spray can.
And my original topic:
Last winter'* recoating:
(while repairing the crossover pipe crack.....my advice is to remove the heatshields entirely for coating)
And what they looked like when the motor was pulled one full season later:
I can get you shots of them as they sit in the car if you like. The shiny spots after recoating have baked to a uniform satin/flat finish, and there are no scratches anywhere, nor any flaking.
The test data in the topic above is still repeatable.