thanks for the info going to start looking into this in few days.With a TH- 350 the 36 element sprag upgrade requires a different drum also.....it's not just a drop in on the stock drum and it is well north of $100. You must be thinking of the TH-400, which does have a $100 sprag upgrade to 34 element sprag.
They are not the same piece.
The relatively inexpensive 34 element sprag for the TH-400 will not fit a TH-350.
The good TH-350 sprag only comes assembled on the drum, since the inner stock race has to be modified to take a 36 element....and it is a $300-400 piece. $550 if you want a steel drum rather than cast iron.
TH350 Drum 36 Element Sprag 350-327900 TSR Racing Products (tsr-racing.com)
BTE Racing: BTE TH350 Heavy Duty Drum w/ Sprag
Transmission Specialties | Transmission Specialties (tsirace.com)
TH350 Iron Drum/HD Sprag Assembly (tciauto.com)
It was not included in this level of trans from TCI, you have to buy a transbrake equipped model from TCI to get the good high power drum and sprag.
All TCI puts in this level of trans is a new roller clutch package with HD springs and a hardened sprag race....not really all that much stronger than stock really. Still only 8 or 10 contact rollers in that stock style roller clutch/sprag.
Just the hardened race is $100 bill...
TH350 Intermediate Sprag Race‚ Hardened 350-35732HD TSR Racing Products (tsr-racing.com)
And the roller clutch, $70
All Products (tsirace.com)
I had a 450 hp 383 SBC break 3 straight so-called "hardened " stock style sprag races in a fresh manual valvebody TH-350, 6 to 7 1/4 mile passes each before I got smart and bought the good drum/sprag package....never touched the trans again.
And this was just a low 12 second pump gas 3600 lb street car with soft compound 8" wide dirt track tires on it("cheater slicks').
You've already got the trans....but TCI would not have been my choice at all for a trans builder.
You'll have to find another stock drum if you are going to try the new stock style roller sprag with a new hardened race and put it back together(I don't recommend it, you are paying more than 1/2 the cost of just getting the good drum )....blowing up a stock type ruins the drum for re-use.