New member AND a clucth judder issue!

[sam1905]

Hello everyone,
It is great to find this community as similar forums have helped me over and over again with other cars and motorcycles. (BMW 2002’s, Aircooled 911’s, airhead BMW’s etc etc).
I grew up in the UK loving the Fulvia and finally found one in the last few months and could not be happier! 'Bruno the brown car' is a 76 Fulvia 1.3.
At 6’6” there is a very small overlap in the Venn diagram circles of “Italian cars I love’ and ‘cars that I fit in at 6’6” and this works perfectly! (I did design some custom seat brackets and had ‘Send-cut-Send’ cut and bend them for me)
I have been getting to know the car and have an issue I would love thoughts on. The most worrying symptom was yesterday when after around 30 minutes spirited driving in the mountains I started to have a VERY pronounced ‘rumble / judder’ on up shifts. These seemed worse 3rd – 4th but also were there in other gears and felt like driving over a very pronounced concrete rumble bar for half a second or the entirety of the clutch engagement (5 or 6 good ‘hops’). I then let the car sit at a cars and coffee for an hour dreading the long drive home, but the problem did not repeat (yet).
Some other information that may or may not be related but as it pertains to clutch feel I have added yesterday.
The clutch plate seems ok when engaged, I can put the car in 3rd or 4th and lug up long hills around the max torque point and there is no slip. I do not know when it was replaced but as much of the car has recently been renovated it may be newer.
When cold the car needs to really be babied from 1st to 2nd to avoid a crunch, better when warm. To a lesser extent all shifts need to be far slower when cold. (as with many cars…)
Despite all engine mounts being new there is a sense of a slight mass shift / rocking when coming on and off the gas from a trailing throttle. (A soft clunk /clunk that I would normally attribute to engine rock..)
Before I go down what seems a tricky path of getting at the clutch, I welcome any thoughts!
Many thanks
Sam