A splendid haul for £7!
The clamp block should fit around the fixed stem, NOT the plunger, of the DTI, to clamp it to the rod on the G clamp, or the holder in the RH bottom corner of the box.
If the "Monkey Block" will mot do this, you can always make a suitable clamp in your shop.
Use a piece of 1/2" or 12 mm square bar and with a bit of drilling, tapping and hacksawing yo will have a bespoke one! If you want to make a really neat job, copy the existing one, to amended dimensions, to clamp the DTI to the rods, and make a really smart job by knurling the thumb screw.
The lever arrangement is particularly useful. It will clamp around the stem of the DTI and allow it to be used to clock bores.
Another project to go on the Round Tuit!
If the centres won't clean up particularly well, they can always be used to centre work in a 4 jaw chuck using the "Two Centres" method. Assuming that there is a centre drilling in the rear end of each one.
(There's a picture of this on the front cover of Tubal Cain's "Simple Workshop Devices" No. 28 in the Workshop Practice Series. )
Howard