petrol to 1y waters pipes help

[campercrazy1]

hi, nearing the end of the 1y conversion and a lesson learnt- start with a diesel van, or have a complete diesel scrapper nearby!

anyway, gotta hook up the water pipes, the radiator and the heater ones

but they are different diameters, , not soooo worried about bodging the rad ones, but what about the heater ones, did people use copper? or can your buy 'stepped' sections of tubing somewhere to go from small to big

any ideas greatfully recieved as always