Well Roger you have got what are termed the Cooper heads if they have 11 studs they were also used on the certain Metro`s and Maestro`s but without the bypass outlet although if it had the screw in blank it can be changed fairly easily.
The valve sizes might help in telling you what the heads came from.
Standard 1275 inlet 1.313" exhaust 1.151" castings 12CC,12CE,12V
11 stud 1275 inlet 1.401" exhaust 1.156" casting 12H199
Cooper 1275 inlet 1.401" exhaust 1.218" casting 12A185 - AFG163
The 11 stud spec head was also used on other transverse engine cars such as the MG 1300, 1300GT as well.
Hopefully this will help you find out what the heads came from as it looks like your are the larger valve sizes and will certainly involve pocketing of the block on the 1098 engine, as for the 948cc is such a large valve head suitable.
Once you have popped a couple of valves out look at the seats, you may need to clean them and if they are unleaded you will see the ring of the unleaded seat inserts, you may have to look quite closely.
Dont know about the rocker shaft differences can you not measure the valve spacings of the different heads to see if they match ?
So it looks like you may have a pair of the larger valve heads
rather than the standard 9 stud one, all the above info does rely on standard size valves and if the heads have been worked on other larger sizes are possible.