Shell Ultra is API SN/CF grade. Why'd you want CF when CH, CI with a greater TBN is available at half the price?
And don't go anything fancy like LM, especially at 20w50 viscosity. IIRC, Delo Gold had more OEM recommendations than any other diesel spec oil in Pakistan, and it's cheaper and very well tried and tested- so what's wrong with that?
Or if you want something different, you can try ZIC 5000 API CI 10w40, but I'd stick to Delo.
a. One can of Ceratec is not enough for 7.3 litre oil sump.
b. I thought it lasts for about 50k kms?
c. Sorry to say, but what's with all this LM fever? I wouldn't use any thing you've described here.
You're not advised to switch viscosities so often, and I don't recall a proper w30 diesel oil being sold in Pakistan anyway. Synthetics, being sold here, are generally SN oils with CF grades. They are inferior and more expensive than a proper diesel oil.