Sorry about your additionial problesm. Your test pressure sounds to be at a good number, but it will change in the different gears. So, it will be different in 1st, 2nd, neutral, reverse, and 1st gear with the transbracke applied. There are several different things that could be causing your problems. For it to blow out the front seal, it is getting too much pressure built up behind the seal. I drill the hole beside the stator out to 1/4" and this helps fill the converter faster and helps on the excessive pressure behind the seal. This can be seen in the articles done in the DragRacingOnline article
http://www.dragracingonline.com/tech.../viii_1-1.html
http://www.dragracingonline.com/tech.../viii_2-1.html
JW also sells a powerglide repair manual that I have used for several years with some benificial tricks.
The reverse clutches could be too tight. I set them up with 0.060"-0.095" clearance and all of the springs. The reverse dump in the case may need to be enlarged to allow a quick release. If reverse doesn't release quickly it can cause your 60ft times to be real sluggish. On the JW case, I was told that there is an adjustable bleed dump to allow it to be quicker or slower on the release.
If the high gear clutches are too tight or partially being applied it can cause a drag, also. I set their clearance to about 0.050". I use the double ring servo in the case. When low is applied it pushes on the apply of the band and the release of high gear. Then when high gear is applied it pushes for the high gear clutches and pushes on the release of the band. This is through the little steel tube that goes from the transbrake/valve body to the transmission case.
If your trans cooler is too small or it is stopped up, it can cause a back up and cause a problem with the release and cause problems with the front seal.
If the front drum has been machined for a roller bearing the end play can be tightened up to about 0.010".
I use all straight steels and no wave plates in the clutch packs for racing.
When you have problems with the Transbrake not holding, what RPM are you at and what does it do (rock backward or rock forward, or drive forward)?
Thanks