Gearbox mounts?

Just come back from an overnight trip, around 200 miles mixed motorway down to single track. Getting a lot of judder pulling away with the transmission jumping about. Clutch should be good, and gearbox was ovehauled a while back, but I don't recall fitting new gearbox mounts. Engine mounts are about 2 years old. My plan is to change gearbox mounts first. Struggling to work out part numbers. Its LWB S2A on military chassis (removable cross member) and with the tie rod to the chassis. Its got the 3.3L (weights a ton) Perkins in but I'm assuming that as the transmission is standard the mounts will be too. Any other things to look out for?
thanks

DONT USE BRIT PART ONES FOR GOD SAKE
check prop ujs and splines

I see there are square and round mounts?

Progress report; got time to go and look. Square mounts, one loose and one dropped. found a spare in the shed (pity there weren't 2) so changed one and tightened the other. Has defenately made a differnce but I suspect there's also a lot of backlash in the drive train. UJs and splines are good, culprets are diff and box so I'll live with it for now. Puzzled by the mounts being loose I took it off with the bracket to tighten it on the bench and found the problem was the way the studs are welded to the mount and there's a small lip, this binds on the hole and gives a false feeling of being tight. Took both brackets off and put in a 1/16" shamfer on, fitted much better.