There are a number of factors you might want to consider.
Firstly what size tools/toolbits do you want to use. I eventually settled on 6mm/1/4" and 4mm square bits normally using a 3 or 4 inch length cut in two. For most work the 4 mm was adequate and minimised griinding.
Secondly you will want to reduce the amount of packing required. A solution here is too make a two way tool post, like the one in the photo above* but with two slots. you might combine 6 mm and 1/4" or 6mm or !/4" with 4 mm. etc.
Thirdly I would determine the centre height by direct measurement over the cross slide top, You will need a centre or similar to fit the head stock bore. preferably with a measureable diameter and then do the maths for each tool bit size.
Another trick would be to use a three or four way post with the registers cut stepwise.
* was a standard item find a catalogue on line to see arrangement.
Hope this helps
John