The fix is complete. Thank you for everyone who answered, contributed and lend a helping hand with this project.
I took my time, drained the coolant all the way and since I had already committed to taking the tank off, I did.

But I think it could have been done without removing the tank if careful to not get shavings into the coolant reservoir.

The brass fitting went in really well and seems as solid as a rock, backed up by JB Weld as a thread sealant. Could probably have used plumbers tape.

Either way, the SRT reservoirs are not available.anymore so hoping one day Needswings makes one out of metal. Till then this is probably as good as it gets because a used one will also fail. I also purchased a new hose going to the fitting so there would be less pressure on the barb fitting. The original hose had the broken off plastic/brass nipple stuck inside and when I cut that off, the hose was too short for my liking and too curved, so it looked like it might put added pressure on the fitting.
Hose purchased at NAPA for $6, fitting purchased at local ACE Hardware $3.80. Well worth the time and effort and if I did it again, could probably do this in 30 mins.