fitting an trailblazer motor and transmission in an old truck

[watahyahknow]

ok heres my hairbrained idea :

i have a 1979 shortbed squarebody that originally came with a line 6 engine
the registraition still saying L6 and to stay out of trouble with the law i want to take out the 305 / th350 V8 thats in it now and replace it with a straight 6 cilinder 4.2 liter out of a 2002 trailblazer
doing this prevents me from having to go to the dutch DMV and possibly loose my vintage car registration or perhabs even the complete registration on that truck making it illegal for me to drive it

now the plan is to buy a complete trailblazer donor vehicle and basicly change over the engine transmission wiring ecu and some of the interiour intoo the chassis and body of the old pickup

now the ecu will prolly be going nuts about the fact it cant find the original trailblazer dash the abs signal the ignitionkey signal and the airbags amongst other things
does anyone know a company that can take out those things out of the software of the ecu so the engine and trans will work without those signals ?
or sell an ecu that will work out of the box with this setup