will rockers off a small bore motor fit on a 1275 12g940 head i have a set of plain 1098 steel ones (top pic)and also a later type a+ ones (bottom pic)
the a+ rockers dont seem to line up in the middle of the top of the valve only some valves

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77 Leyland Clubman
1293cc, LCB extractors, pulsar dizzy (recurved), cooper s disc brakes, 40DCOE Weber

They will all work on a 1275 if you fit a flat washer next to the exhaust valves ONLY.
Valve spacing on a 1275 head is different, as the valve heads are bigger.
The A+ rockers were used on 1275LS etc, with a washer as I said.
<edit> they still don't line up properly, but they work.

Those top ones look like 1275 not 1098, as the pads are oval.
1098, 998 and 850 had round pads.

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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.

is it a special washer or just put a flat washer that lines it up

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77 Leyland Clubman
1293cc, LCB extractors, pulsar dizzy (recurved), cooper s disc brakes, 40DCOE Weber

Just a flat washer about 1.5mm thick will do it.
I use 12mm ones and bore them out. It's hard to find proper 9/16" ones these days.
14mm ones if you find any are usually too loose.

Valve lift and rocker ratio:
The top ones in your pic are best.
The bottom ones are 2nd best.
the S rockers in your middle pic are worst for lift, and vary quite a bit.

Note if using the A+ ones- check their bores are not worn oval. If they are OK I would fit with a new shaft. These crap design sintered rockers have no bush, so cannot be repaired.

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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.

I had a sintered one break on me once, i had just turned into my street and went to drive the 30 metres to my driveway when it happened. Pretty lucky to break within pushing distance from the house Apparently they aren't very good for racing either.