Topic: 1975 CB400

[Islandstar]

Hello from Barbados. I'm new to this site and to this bike. Picked it up yesterday from mechanic. Rides well but right away I think I would like to do a pod mod and maybe change tires. I'd like some help with a few things....what size pods and jets I need, how hard is the job, and the biggest tires that will fit. I have moderate DIY skills, as I have done some work on my V Star.

[Smoke Detector]

Welcome.
Regarding pods, you can find lots of info and discussion, both for and against, by using Google chrome search on top left of this site (do not use top right search box).
I'd suggest asking yourself why you want to change to pods if bike is currently running fine? I have no opinion pro or con about pods but I'd be tempted to just enjoy the bike as is for now. But your bike, so your call. 
As for tires, again the search function and FAQ section have lots of info, and also many members here have the expertise if you have specific questions.