Gearbox not going into neutral

Got the gearbox back together going by the book but something's not quite right. Gear selection is a bit stiff and if I put the stick into neutral its still transmitting power to the rear output shaft if I turn the input shaft in the bellhousing.

Its also very stiff trying to turn it in reverse and to select third gear

Any idea what could be causing this? I had thought it would be gears tight on the mainshaft but the clearances are to what the manual says, they're tighter to rotate than my old gearbox but I thought that would be wear

Worth mentioning this is just turning by hand with no oil in it as yet, but all parts had oil on them going in. I dont want to chance it and put it in the landy only for it to self destruct setting off

Its a suffix A box by the way

Check all your selector forks are sitting in the correct grooves.
Did you fit the 3rd / 4th synchro unit the right way round.
If you hold the rear out put shaft still can you turn the input shaft when in nuetral?

When you say transmitting power - how much?

Can you stop the output but still turn the input?

if it's definitely in some gear or another it's time to yank the forks and see who's not in the right place.

I think its definitely stuck in gear so will have a poke around with the selectors withmy granddad tomorrow after work.

Synchro hub is in the right way round (with the recessed end facing third gear)