Im glad that someone is looking at turbocharging the good ol Maruti 800. Its not that bad and its definitely fun for sure if you get around setting it up well.
I presume your M800 (1998) is a carby and not fuel injected. Getting a carby setup to run turbo is a bit more tricky that to do a fuel injected turbo setup.
I did a M800 carby turbo setup about 5yrs back and now running another Fuel injected M800 turbo setup (Daily drive). Both were fun projects and not meant for racing. It was much more challenging to get the carby turbo setup working well as compared to the fuel-injected M800.
You may want to consider these points if you are planning on turboing your carby M800 -
1. Decide if you want to go "Blow through" type or "suck through" type turbo setup.
(Both have their own set of challenges to say the least)
2. Preferably opt for a positive manifold pressure friendly carburetor if planning on a "blow through" setup. (Stock/OEM
carby may bleed petrol from different places when on boost)
3. Decide on a good Turbo suitable for small displacement engine -
eg for street setup - IHI RHB3, IHI RHF3, small Hitachi unit, KKK KP39 ..... and the likes.
4. Fabrication -
a. Fabricate adapters/flanges for the new carburetor.
b. Fabricate new turbo exhaust manifold and turbo bump pipe + high flow exhaust.
c. Fabricate intake plumbing considering the location of your intercooler (TMIC or FMIC)
5. Check if you have any option to buy ignition control unit that will help you to pull out/ retard timing with the onset of boost. You can do a build without it provided you are not planning on high boost.
From my personal experience turbocharging few cars including my present Baleno turbo and M800 MPFI turbo, its much easier to setup a fuel injected turbo setup with the help of a good Piggyback ECU or a stand alone unit with the help of someone who can help you tune it for the right AFR and igniting timing.