There are some good threads on Mud about the conversion, this is a popular one:
https://forum.ih8mud.com/threads/minitruck-front-axle-disc-brake-conversion-for-dummies-faq.137225/
As there are so many different master cylinder combos and donor axle combos, it would be tough to have a one-size-fits-all disc brake thread but the one above is likely the most helpful in terms of the basic scope of the job. Pre 70 stuff is much more difficult as they don't even have a booster and have a single circuit brake line. However, with your 74, you simply bolt the 76-80 master to your existing booster, 100% the same bolt pattern. As that cylinder was made for the disc/drum combo that you now have, they generally do not require any proportioning. If you do an upgrade cylinder such as the FJ80 cylinder (1" bore), then you will need to proportion the rear circuit using a common in-line proportioning valve (Wilwood for example). I say generally as there are a variety of calipers out on the market with different cylinder sizes too. The mini-truck ones are very similar in size to the FJ40 original option so the cylinder should leave you just like stock. If your donor axle had later or upgraded calipers, you need to proportion to balance things out nicely. Honestly folks usually just call us and we send them out a batch of the parts they need based on the core axle and year Cruiser they have, we setup a customer or two each week as disc brake swaps are still extremely popular. I always prefer a customer sourcing their own core axle (knuckles, spindles, hubs, hub bodies, rotors, calipers, etc) and we can get everything else needed brand new. Some companies are still selling GM parts for disc brake conversions using machined rotors and bolt on caliper brackets, that adds to the confusion a bit more.
With a mini-tuck donor axle you will still need to sort the steering arms (40 Series is smaller taper than the mini-truck tie rod end), we have a solution for that too by way of a spacer. Lastly you'll need to modify the brake lines but that is easy stuff and we stock all the different hose lengths needed. Beyond that, axle clips (you'll be swapping the birfs to your existing inner axles), a knuckle seal/gasket or overhaul kit and some elbow grease and you're in business.
heheh