More of a problem is that once you've got it out you can't really just swap the half shaft for one from an electronic speedo box. The diff clearances are set by the shims between the half shaft bearing housing and the gearbox case - you can see them on the outside of the box. If you change a half shaft you need to reset the diff clearances to spec, breaking out the dial gauges and so forth. If you don't, the diff will likely be toast in no time. Please don't ask me how I know.
I had a look at one of my old halfshafts today, which I replaced on my old geabox with another used item because the halfshaft bearing was loose and allowing oil past the seal. Note that I have driven something like 10,000 miles with this new assembly in place with no problems.
SV is completely correct about setting up the diff clearances, but removing the halfshafts does not affect these clearances - the halfshaft has a spline which engages into the differential, and the diff itself is located in the casing by bearings, so that the crucial relationship between the crownwheel and pinion is maintained. The only thing you MUST ensure, when swapping the halfshaft carriers, is that the splines do not "bottom out" in the differential. This will certainly cause the problems that SV notes above, and is the reason why there is a split shim fitted to space the halfshaft carrier away from the gearbox casing.
So I would suggest measuring the length of the Sprint and 33 halfshafts and use whichever set of split shims you need to prevent the halfshaft from bottoming out in the diff. I am pretty sure once you have the two assemblies side by side you will find very little difference between them, and you will be able to use the 33 halfshaft, carrier and phonic wheel in your Sprint gearbox.
The bearing retaining bush removal tool described by SV fits over the bevel gear/phonic wheel and engages on the threaded bush behind it - so it pulls the halfshaft retaining bush AND the bevel gear/phonic wheel off together. That's going to need a lot of force!
Glad to hear you got the gearbox out OK. All the manuals I have read suggest taking out the engine and 'box as a complete unit, sorry you found that out the hard way!