[oil pan 4]

I went through and really read it.
For the glow plugs loose the controller. When it fails the glow plugs will stay on until they all burn out. Replace with a manual switch.
I didn't see where you said why glow plugs you installed, I highly recommend 60G glow plugs. They cost a few more dollars each than the stock 6.2 glow plug but my 60G plugs were installed in 2007 or 2008 and I have not had one go bad since then. The old 6.2 plugs I was replacing about 1 set per year at $80 a set from 2005 to 2007 or 08. I think the ones that burn all the out all the time have a part number something to the effect of 9G, 11G and 1110. I highly recommend replacing these right away with a 60G plugs and a manual controller before you get stuck some where with burned out glow plugs. Or at least buy a set of 60G plugs and 10mm wrench, keep them in the truck.
You mentioned a th700 swap. The problem with that is to go from a th350 to th700 you will have to have the TV cable holder which is almost impossible to find for the diesels. I have already ruined one th700 due to improper TV adjustment when the previous owner swapped in a different carburetor on a camaro right before I bought it with out the adaptor for the th700 TV cable.
Also the diesel th400 has 6 bolts between the flex plate and converter. But you should be able to use a gaser th700 and torque converter if you have the diesel TV cable holder.
If I decide to go with a 6 speed I will be selling my th700 and related parts. But the transmission has no lockup for some reason, it quit working last year and I just have not been driving it much.

For a boost gauge I highly recommend a boost vacuum compound gauge normally used on turbocharged gasoline engines. That way you if you have an exhaust leak before the turbine, the intake will be pulling a slight 1 to 3 inchs of mercury vacuum when you first start going from a stop.
For a pyro, get one on sale from ebay, that's what I did so you don't have to pay $200 or more for one.