Vendors and private owners have been making undercar water pipes for decades. So not all stainless pumbing 'kits' are the same- and some are not even stainless. Some early ones in the ;70s were thinwall copper, apparently for a little more heat radiation. That turned out to be another un-good addition to Panteras unless you insulate the console!
For the engine ends of my 20+ yr old stainless tubes, I used 90 degree copper sweat-solder fittings 1-1/2" OD. Std 1-3/8" gates hoses can be expanded enough with heat to slip on. No leaks in this century.....