Martin spring and driveshaft right here in Kalamazoo does a great job with driveshafts and high speed balances them too. Very reasonable, never had an issue or hurt one with anything i have had

69 Dart GTS A4 Silver All steel, flat factory hood, 3360race weight
418 BPE factory replacement headed stroker, 565 lift solid cam
Best so far, low 10.30’s 1/4
1.41 best 60 foot
6.56 at 104.17