Whats the best Valve Guide to use
Cast Iron or Bronze

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1970 MK2 Cooper S

cast iron guides for normal valves
bronze guides for stainless valves
"Generally"

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No offence intended here but--> anyone writing a book about minis 30 years ago may not have experienced such worn or stuffed-with components as we are finding these days.

You should put your heart & soul into everything you do.

The original cast iron guides but with k-liners fitted. Not cheap, but they give best heat transfer and run minimum clearance.
Work fine with stock valves or SS ones.

[edit]
re bronze guides, I do run a set in my car. These current manganese bronze ones tend to shrink when fitted, definitely need a 9/32" reamer through them after fitting. And one of mine even then tried to grab an exhaust valve when first run, so I had to pull the head and ream them a second time. To be sure, to be sure...
That was 50,000 miles ago (with 1.5:1 forged rockers) and they are still working fine.

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.