Dipsticks, A and A+ differences
The A and A+ dipsticks are different.
The A+ sits straight in the block and A series one sits in a tube that sits in the block. The distance from the seal to the max/min markings should be the same, but the length of stick from the tip to the seal is different. Beware that you have the correct one for your block; the distance between the tip and the "min" mark is longer on pre-A+.
Dipsticks, using A in A+ and vice versa
The distance from the block/box flange to the sealing ring on the dipstick when inserted is the same on an A or A+ engine (~10 cm).
The A block has a tube (7cm of block plus 3cm of tube).
The distance from the sealing ring on the dipstick to the maximum mark is 23cm for A and A+. The distance bewteen min and max is ~10mm on BOTH.
BIG problems will arise if you try to use an A+ (thicker sealing neck) dipstick in a A series block by removing the narrower dipstick tube, the A+ dipstick mounted DIRECTLY into the A SERIES block would be 3cm deeper into the sump and minimum would be shown with approximately 1.5 litres less oil in the sump as the 1cm minimum to maximum equates to 0.5 litres. This would not be good for the gears!
DO NOT RUN A DIPSTICK IN A BLOCK WITH A BOX/BLOCK FLANGE THICKNESS OF 7CM WITHOUT A DIPSTICK TUBE!