KB, let me add some clarity for you if I may.
In post #2 above, the schematics can confuse some owners in that they mention "Short Shaft" "Long Shaft"!
The 250, 270 and 275 all offer one exposed shaft length (when absent the spacer/line cutter).
The 280, 285, 290, SP and several others, all offer another exposed shaft length (when absent the spacer/line cutter).
Here is what's commonly misunderstood:
The 250, 270 and 275 all require the
short spacer/line cutter.
The 280, 285, 290, SP and several others, all require the
long spacer/line cutter.
Hre is the important part: Either nets the exact same exposed prop shaft spline dimension, but only when the correct and mandatory spacer is used.
With only one limitiation, this means that any hub prop (long or short) can be used on any of these lower units.
The exception is when we get into the long hub prop on an early lower unit that does not have the internally threaded prop shaft.
This has everything to do with the style of spinner (aka cone nut) keeper or locking system.
Since the long hub prop prevents the shaft from sitting "proud" of the hub, the SS tab washer can not be used.
This limits us to using the center keeper bolt.
The center keeper bolt works only with a threaded prop shaft (275, 280, 285, 290 etc).
IOW, without the internal threads (250, 270), the AFT-most portion of the 2 pc spinner cannot be used with a long hub propeller.
Well, it could, but we'd have no means of locking it!
If you indeed have a 1985 drive, it is more likely a 275 drive...... not a 270.
All 275 lower unit prop shafts offer the internal threads, and the exhaust outlet that is placed further AFT.
If you have a 275 (sounds like you do), this would mean that you have more propeller choice options.
NOTE: The spacer/line cutter must be used! No exceptions when using a propeller designed for these V/P drives!
The spacer/line cutter must be correct for the drive model, not the propeller!
NOTE: The sum of both halves of the 2 pc spinner, equals the 1 pc spinner dimensionally.
Difference being, that the AFT-most part (of the 2 pc spinner) reaches into the long hub propeller in order to fully thread onto the propeller shaft.
Without this, the long hub propeller cannot be used.
Point being... don't confuse yourself between prop shaft lengths!
As said, all of these net the same dimension of shaft splines
when the correct and mandatory spacer is used.
Instead, concern yourself with the correct spacer/line cutter, the hub length and the type of spinner that can be used.
The 2 pc spinner gives you more options, but again, only if your prop shaft is internally threaded since the SS tab washer can't be used with the long hub.
Make sense?
.