Gear selection problem.

[Ralphypants]

Hi everyone, hopefully someone can help with a problem I have. I recently bought a vw gpr1 Jas beach Buggy 1972 with a rebuilt 1974 Range Rover 3.5 V8 engine with high lift cams & a 4 barrel Holley carb( covered 600 miles). Race clutch (new) & 4 speed short shift vw gearbox.
The issue I have is that when the car is up to temp 90c & has been driven well for 30 mins the gear selection which was fine is now notchy. When selecting 1st you can hear a bit of a crunch even with the clutch pedal to the floor. Several times I can’t get out of 3rd of select any gears from neutral, all is back to normal when the car is cold.
This car is unbelievable fun to drive only ruined 30-40 mins later with this gear change problem. Does anyone have any idea what the problem could be so that I can get on with having fun!
Thoughts so far are,
clutch cable stretching under heat.
Spigot bearing.
Wrong or insufficient oil.
Gear box knackered. (Told it’s good)
Clutch knackered. (Told it was new)

Also what other gearbox would fit into this vehicle so I can have 5 speeds & pull away quick in 1st whereas I can’t with what I have as I was told I would reduce the gearbox to scrap.
Your thought or better still a solution to this problem would be greatly appreciated.
Thinking caps on, hope to hear back soon.

Regards
Ralphypants.

[Ralphypants]

Thanks for your comments on this issue. Annoyingly it goes into reverse fine so does this mean it’s gearbox? I suspect it is as mentioned here. Why hook up a standard 46 yr old vw box to a souped up 3.5 V8 , what were they thinking!
Would another gearbox fit in or do I have to go with a Rancho type?

Thanks for getting back to me.