67Jet,
I did a lot of research on this subject when considering my suspension conversion. I just did the conversion in April/May from stock MGB to the Hoyle system on my Arntz. I posted on the Arntz forum
LINK at that time my reasoning for going Hoyle vs Fastcars.
I'm pretty happy with my choice and my assumptions have proved correct. I'm still dialing in the spring rate, with my big block I had thought I would need heavier springs but this has not proved to be the case. I'm currently running 400#'s, since I also have 300# & 350# sets, I'm going to go to the 300# next.
Let me know if you would like to discuss this in more detail.
BTW: SoTxButler your suspension looks great, if I had the $$$budget I may have gone your route, but as I said I'm happy with my results.
Mike