Just done this myself as I'm also rebuilding a 4 synchro (my first one).
I just moved the selectors using a brass drift and long screwdriver.
Here's a couple of pics to show you what it looks like when first and fourth are locked up (after removing all the innards to actually get up to this point);
Below is the position of the selector rod ends when the gears are locked (the bottom one shows first gear engaged when it is fully to the left and the middle one shows fourth gear engaged when it is fully to the right-the upper one is the reverse selector rod);
Here's a pic of the gears when first and fourth are engaged (first is engaged on the left and fourth is engaged on the right);
And here's a pic of the gears just before you engage them from someone else I found on the web (you need to move (1) to the left and (2) to the right to lock up fourth (1) and first (2).
Pretty sure I've got the gear positions correct but hopefully others will let us know if it isn't (it worked for me).
I used a rattle gun and deep sockets to remove the nuts BTW, it was a bloody lot easier than a breaker bar with an extension and someone standing on the gearbox.
Cheers
Dave
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