Not weighed all the tinware but a stock oif A65 is about 100lb. There’s a lot of tinware on there which could be removed, light alloy tank track master style. Aluminium barrel. Simplified cdi ignition removing the heavy alternator setup, wiring, switches, lighting etc etc.
You could also fit a SLS front brake off the b25/B50 with its matching right hand fork leg. Again much smaller and lighter and for off road you don’t want a well braked front wheel. Alloy rims.
High level or TT
Exhaust without silencers. Fit the louvered inserts if you want some form of silencing.
If you do all that you’ll probably get below the 300lb mark. I think the engine weighs about 160lb in standard form, much lighter still with the previously mentioned aluminium barrel.