Do the B21 retainers weigh less then those big Isky retainers. Are they made of good metal?

I dunno, I've never weighed them. Is the metal good? I guess so. :)

In the past I've also made them out old Datsun or Toyota retainers, I've never bought aftermarket bits because the Aussie dollar was garbage compared to the greenback in the late 80's + I was still on apprentice pay of some sort.

Before making the exhaust ports decent I use to use just 4 duals on the inlets & stock springs on the exhaust, coupled with a high lift sort of inlet lobe only. Them was the days.