OK, engine problems solved Most problems was caused by old hv wires... so I put new set and now engine works great. Soon I should have some new tires on rear (old ones are slicks right now). and I have to change few parts in stering.

 

Some new photo

 

Those LPG tanks seem to be smaller than the CNG ones used in my country, so eventually you might be able to fit it in the original location of the spare wheel without having to remove the rear sway bar as it's usually done here when a Blazer is converted to CNG with underbody tanks.