Hi all, after having an issue with a blocky deck and resolving it I thought I would share it as it may be a common issue.
The heads were not raising far enough and allowing the tyre wheel to engage the take up spool and thus playing a tape. After investigating whether it was being caused by the deck head spring issue I could see that this issue was indeed present but was not the reason for the heads not raising, so one thing at a time, lets get the heads being able to move far enough up first.
After investigating the deck a bit and taking the back plate off along with fiddling and trying to raise the heads manually, I could see there was a piece which was stopping the heads raise any further.
The front plate must be removed to see the deck front.
The photo below shows the take up spool and tyre which engages it inside the red circle and the problem causing the heads to stop short.

Below is a look at how the take-up spool is engaged by the heads raising and the small lever above the yellow arrow dropping into the narrower gap on the head plate beneath the red arrow as it moves upwards. When the lever moves into the space the tyre engages the take-up spool and makes it turn.

A closer look at the little notch which seems to be resetting after manually moving the gears and flywheel. This is where it should be resetting to but as you can see in the picture above that it is resetting too low.

Looking at the reverse of the deck and carefully removing the security plate for the flywheel and the flywheel itself, you can see the lever which is related to that little notch on the front. At this stage you can determine that it is related to the pause function. This lever lowers the notch on the front and subsequently lowers the head plate. Trying to manually move it was difficult because it was stiff as hell.

Removing the shoe clip on top and sliding the lever off revealed a pretty dirty and grim looking pivot post,

I basically cleaned that post and inside the hole on the lever to provide a smoother contact, put it back together and tested manually that the lever would be easier to move and it was.
if you have this issue, don't automatically assume that it is related to the head spring issue (which can be read here - https://boomboxery.com/forum/index.php/topic/13086-ge-3-5259a-blockbuster-play-not-engaging-ff-rw-pause-fine/ )
Incidentally, the pause button and mechanism worked fine, its just that the lever behind the button stays in the on position and doesn't reset when pause is taken off again.
Hope this might help others fixing their blocky decks.
The heads were not raising far enough and allowing the tyre wheel to engage the take up spool and thus playing a tape. After investigating whether it was being caused by the deck head spring issue I could see that this issue was indeed present but was not the reason for the heads not raising, so one thing at a time, lets get the heads being able to move far enough up first.
After investigating the deck a bit and taking the back plate off along with fiddling and trying to raise the heads manually, I could see there was a piece which was stopping the heads raise any further.
The front plate must be removed to see the deck front.
The photo below shows the take up spool and tyre which engages it inside the red circle and the problem causing the heads to stop short.

Below is a look at how the take-up spool is engaged by the heads raising and the small lever above the yellow arrow dropping into the narrower gap on the head plate beneath the red arrow as it moves upwards. When the lever moves into the space the tyre engages the take-up spool and makes it turn.

A closer look at the little notch which seems to be resetting after manually moving the gears and flywheel. This is where it should be resetting to but as you can see in the picture above that it is resetting too low.

Looking at the reverse of the deck and carefully removing the security plate for the flywheel and the flywheel itself, you can see the lever which is related to that little notch on the front. At this stage you can determine that it is related to the pause function. This lever lowers the notch on the front and subsequently lowers the head plate. Trying to manually move it was difficult because it was stiff as hell.

Removing the shoe clip on top and sliding the lever off revealed a pretty dirty and grim looking pivot post,

I basically cleaned that post and inside the hole on the lever to provide a smoother contact, put it back together and tested manually that the lever would be easier to move and it was.
if you have this issue, don't automatically assume that it is related to the head spring issue (which can be read here - https://boomboxery.com/forum/index.php/topic/13086-ge-3-5259a-blockbuster-play-not-engaging-ff-rw-pause-fine/ )
Incidentally, the pause button and mechanism worked fine, its just that the lever behind the button stays in the on position and doesn't reset when pause is taken off again.
Hope this might help others fixing their blocky decks.