I'm not sure about all of the 1098 engine, but for sure on the Spridget 948, and the early 948s, had a metal dipstick tube, like the MGBs, and the dipstick on the early A-series engines did not have the dipstick stop ring on them like the 948 and early 1098 did, they rest on a factory indention in the oil pan, you can't interchange the 948 dipsticks with the 1275, in a 1275 the 948 dipsticck will rest on the pan floor and the level mark will be well low.
Hope this helps, I'm sure someone will fill in some of the blanks I left.