If it's still good I'd leave it alone and add the CL-90 under chassis.

Plug it in try it who knows it may work most of those ballast rust up inside and they are just to old and don’t work.

Can't hurt right? I've done plenty to F&$# up this TV. What more could I possibly do to hurt it?

Says it's NOS so who knows. In the original box and packaging.

Is that the ballast for your set because there are 2 different ones.

It isn't, but should work with a minor modification. The '303 has an extra element, but I'm pretty sure the TS-4H doesn't use it.

He will need to move the ac line from pin 5 to pin 6

That’s what I will do.

I noticed when fooling with series string electrostat TVs that the heater would flash on turn on, glow bright, and then subside.
I thought it was due to them not being controlled warm-up heaters in these jugs, including the Pilot 3KP4.
Do I recall correctly?

I believe that's due to the inrush of current. I've always brought this TV and my Pilot up on a Variac.

Yes, it is due to the inrush of current when the filaments are cold. Using controlled warm up version (typically ending with 'A') does not eliminate the inrush current. It simply means it is well defined. Typically taking around 11 seconds for the filaments to warm up.

The series string doubler electrostat should have had a heater transformer on the jug to extend its service life.
Do any restorers do this for working display sets?

Some, though there's a better option. TVS (transient voltage suppressor) diodes (8.2V IIRC) in parallel with the heater will clip the peaks off the AC voltage clamping true AC RMS voltage at 6.3V. I'm planning on installing them in all my series sets next time I can place a mouser order.
The person that came up with this has a great scientific thread explaining how they work/how he came up with it over on ARF.

I'm building Bob's design. Waiting for the resistors. I think all I need to do is move the AC line from pin 6 to pin 5. I have 10 of the "Littlefuse" in the appropriate size for this TV. Bob's design incorporates a CL-90. Will that be enough to protect the TV from the surge?

CL-90 yup it will.

I built Bob's design for the replacement ballast but the CL-90 hasn't arrived yet so I bypassed it with a jumper and brought the TV up slowly. I'll solder it in once it comes. The image on the picture of the screen is not what it looks like. The bright area in the picture is spread out in a 3-4 configuration across the entire screen face. There's no video signal through the IF as before but there's audio.

My next question is does the electrostatic tube and focus in any way affect the installing of jacks for composite video? I'm not giving up on solving the IF issue but I'd like to know if that's an option.