It looks awesome as it is, but with the 2.4TD engine, I'd go down to 31's, it will feel so much livelier and quicker on acceleration!
The 2lt engine is known for being a bit underpowered and those tyres are sucking it away, being as your not using it that much off road I dont think the improved off road abilities out weight making it slower, using more fuel and being noisier on the road. You could even go for an all terrain tyre rather than a mud tyre.
As for your sun roof I wouldnt weld it up, I'd try and find one from the later square headlight models. Their made of glass so dont have the rust issues the earlier steel ones had.
Theres at least 3 people I can think of in the UK who break 70's and sell parts. You could also look on ebay for people breaking them and try and track down a sun roof that way.