I've done it both ways.
Ha-Ha has the bigger 1.219" exhausts (these are MK1 head size, but 12G940 heads have longer stems).
I run bronze guides because these valves are 21/4N S/S with plain stems and will pick up in iron guides.
Barney the 1293A+ has Rover inserts, I got `em shrunk in with liquid N2...

. Valves are all Rover ones with chromed stems, guides are stock cast iron. <edit> exhaust valves are stock 1.156".
I've had the big valves in Ha-Ha for about 10 yars now, no problem. I run Flashlube in it.
Not much to choose really, both work, there is no problem with the unleaded inserts for road use if properly fitted.
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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.
