Std cable is 4 gauge (110A continuous rating), about 25mm2 cross section. $8.90/M from roadtechmarine.com.au
I would replace with 2 gauge (160A continuous rating), about 35mm2 cross section.
Diameter total is 12mm, available in red or black. $14.95/M from roadtechmarine.com.au.
I have bought some for my son's Clubby resto. 3.5M will do the battery cable + starter cable.
You can also use 35mm2 welding cable.
[edit] God knows what current draw is on the Lucas starter. However a Gemini starter which is popular fitment on Minis, draws up to 350A according to its data sheet.
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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.
