12G1316 head

I'm trying to determine if I can rework a head I took
off a 1275 block. Casting is 12G1316 - based on some
catalog/web data, exhaust port extras, and lister
expertise, I'm running on the assumption this is a
73-74 smog head. My little shade-tree-mechanic brain
is baffled by the guides for the intake valves. They
have a rubber upper section sleeving the valve, with a
tiny spring keeper circling the very top portion. They
appear longer than the exhaust inserts. The valve
springs for the intakes are also slightly shorter than
the exhaust springs. Maybe as much as 1/4". Valves are
3.57" long.

Can these inserts be successfully replaced with
anything currently on the market?
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