cowl/front cab corner seam
 

i have replaced the front cab corner on my 55 and do not know what to do about the upper seam at cowl. i can not reach it from the inside to spot weld or plug weld.i was not planning on filling the seams, but that is looking like my best option. i would like to know how to keep the seam. the seam is nice and tight looking..should i use seam sealer only and not really weld it together.that sounds not right.. what have other builders done?

It is a pain to get in behind the seam but it can be done. What I did when I changed my a pillar panels was to clean and prime all the joints then when I was ready to install the panel I did apply panel bond and installed the panel with cleco's. Then the next day I removed the cleco's and plug welded the holes and stuffed myself under the dash and edge welded the upper seam.
I drilled 3/16 holes in the new panel and #40 holes in the cab, so I would get a good weld at those spots too. As long as you weld a spot and quench with a wet rag the panel bond it not destroyed.
It might be overkill but I just can't bring myself to use panel bond alone.

Panel adhesive works great...assuming you haven't already welded in the panel. I use 3M 08115, it's made for bonding panels that have just the kind of flange that you have at the top of that cowl repair panel.

Project-55 is not the first to question the bonding capability of panel adhesive, it takes a bit of time for guys who have felt the need to weld the bejesus out of any piece of metal to accept the fact that an adhesive will do the job by itself. If you use panel adhesive don't weld over it, you are not adding structural integrity and you will be undermining the strength of the already superior bond of the adhesive.

If you chose to weld, then weld...if you chose to bond, then bond...don't do one over the other. That said, if you have the panel fit to the cab you can go ahead and bond the top seam and later, when the adhesive is set, weld the other seams on the panel.