I am at work, so cannot browse around too much at the moment.
The starting point would be the site howstat.com.au. In the statistics/batting section there is a list of all batsmen who have scored more than 50% of a completed innings. We'll find our man there. I'll do that once I get home, if you haven't completed it by then.
One interesting entry to look for would be Asif Iqbal in the Oval test of 1967. Pakistan was 55/8 in the second innings (not sure whether it was followon, though), Asif coming in at No.8 was involved in a world record stand of 190 for the ninth wicket and scored 146 - some 55% of the total.