[David C]

First signs are good - it looks as though it has a disc brake conversion.
Check whether it has an anti roll bar and what engine and gearbox are fitted.
Original engine would probably have been 85A at around 80BHP. Later 100A, 100B2 etc over 100BHP and the extra power is useful on modern roads.
It doesn't look as though this one has had an overdrive added but something to look for.

Bristol gearbox may well be good but now hard to rebuild. Later BWCR gearbox is a better prospect.

First signs of rot are usually in front of base of rear wheel arch. Lower the spare wheel carrier and look for corrosion on the sides of the metal on either side.

If you can drive down a hill on the overrun as long as possible then boot the accelerator. As little smoke as possible out of the back is a good thing. An engine rebuild may easily cost £10k

The car should go where you point it and not veer to the sides over bumps. I would suggest you drive all of the available 401s before you make a decision.