you are wrong, the engine does not need conversion.
veg oil is heated via yes electric element (not reccomended) or a simple head exchager like your car heater or raidiator then this heated oil goes into the pump/injectors via a 2 way switch, very simple.
dont understand your next statment, its very easy to fit any keen diyer can fit or at a fitting center.
cars vans trucks buses tractors commercial boats run on veg oil and have been since the 70s this is very big
many many thousands of people run on veg oil for many years no problems.
just a small selection from a kit supplier there are also a huge long term study data base available run bu the end user!
www.vegetableoildiesel.co.ukA Mercedes 300TD has done 58,374 miles on veg oil!
A Mercedes benz 250 TD has done 62,100 miles on veg oil!
A VW Bus T2/3 has done 93,150 miles on veg oil!
A Ford Fiesta has done 66,500 miles on veg oil!
A Opel Corsa B Combo has done 76,500 miles on veg oil!
A AUDI AUDI -TDI has done 80,000 miles on veg oil!
A VW Golf III has done 65,205 miles on veg oil!
A Opel Astra 1.7D has done 60,237 miles on veg oil!
A VW Golf SDI has done 65,000 miles on veg oil!
A Opel Astra 1.9 TD has done 70,000 miles on veg oil!
A Isuzu trooper (jackaroo in australia) four wheel drive has done 51,000 miles on veg oil!
A vauxhall 1.7td van astra has done 75,000 miles on veg oil!
A Hino FB14 has done 78,000 miles on veg oil!
A Citroen ZX Citroen ZX aura has done 120,000 miles on veg oil!
A toyota 1hz has done 75,000 miles on veg oil!
A fiat ulysse has done 256,000 miles on veg oil!