Speedmaster rim offset for early 60's Ghia

I was wondering if someone might have a suggestion or had any experience with Speedmasters on their Ghia, they come in either a 13mm or 21mm offset not sure what to order.
Its a 64 with a standard beam, no dropped spindles.
Any help appreciated.

good to hear you're back in the game.... 🙂

Cheers mate.

widening the wheelbase is very desirable with a og suspension.
mine is irs and has wide cheviots all round and handles any power

wide wheels are a start...... but rear a little wider than front .....is an enhancement of ride and safety IMO