I tried it with a triumph herald rack it was terrible as the rack has to be really short or bump steer becomes a major issue in the end I went back to good old steering box

Maybe not the answer you were looking for, but have you tried adjusting the front suspension? I have found that with the right toe-out and camber settings there is a good deal of positive feel through the steering. Tyres also make a difference. Not tried a TR4 rack to know how that would differ though, but certainly happy with my setup.

rack & pinion
 

As Tom The Biker said the rack has to be very short, Way back in my not so ill spent youth,I worked at Lotus for a spell,( any body in the middx/herts/essex borders and interested in bikes/cars did so) I worked on the drive line bench moding and putting bits together for Elites(prettiest car you ever saw) They used herald racks,the racks being cut and shut,can't remember anything about the geometry unfortunately.

The GP team were based on site and now and again the door would open and one of the team cars "would bomb off" down Delamare rd. the local boys in blue must have heard,they were only a mile away, but copped a deaf un' This quite often occured when "THE MAN" from Webber came over from Italy to breath on the carbs, was like black magic to us lads!!!

Regards,Keith(misty eyed with nostalgia)

I have seen pics of a rack and pinion set-up bolted to the front of the cross-member I think on swedespeed forum.

As stated above we all know that rack and pinion is "better" than a steering box, but is it really? I suspect that an aftermarket rack and pinion with wrong geometry would be significantly worse than a well maintained original steering box set-up.