Had a few cylinders done in the past, they used thick wall tube, use OEM part
NUT
09159-10065, 10mm stud, cant remember the length of the stud I would have to check my notes, I was charged anywhere  from $100 to $175 depending on who I used, I dont know what HPR charges, who ever you use make sure it is someone that has done many lT500 cylinders and has the equipment to deck the bottom flat, you do loose a bore also, depending on the welder I seen the base decked .015" to .020" requiring AFM thicker base gasket located in the store