These are the spars that I know about:
Early: #1 thru >80 ZSpar (I believe, what you have?)
Mid: <117 thru >304 Charleston
Later (?): >304 Seldon (?) I’m not positive but I think they were all Charlestons til the end (Jay Saxton will know)
I have no idea on 387’s but I’m pretty sure there are Seldon’s as people here have spoken of them. [Editor: My C387 #96 had Charleston Spar]
What I do know is that #117 (at least) through my 199, and probably beyond, have the same masthead casting pictured in the Mainsheet article I did a couple issues ago showing the spinnaker crane installation. I know Paul on 170 has it too. That is the OC2 (Ocean series, number 2) masthead and was used way back in the 80’s on Isomat spars too. Charleston bought Isomat at some point and continued using the castings and extrusions.