Replacing imperial size radiators with metric size ones

[gillpeer]

Hello
I want to change the radiators in my house. The current ones are imperial sized ones with odd sizes such as 1770mm, 1670mm, 1920mm and 1580mm etc. in width. To fit to the nearest metric size, I have this in mind:-
1770 - 1600 (extention pipe 90mm on each side)
1670 - 1600 (extention pipe 40mm on each side)
1920 - 1800 (extention pipe 60mm on each side)
1580 - 1400 (extention pipe 90mm on each side)

If I use long valve pipes (90mm on each side), would this have any adverse effect on the overall system?
Screwfix don't do radiators in 1500 or 1700mm size, hence the use of value extention pipes.
My radiators pipes run through wooden floors, so there is no scope to move the pipes coming through the floors.
Has anyone got any alternative idea?
Thanks

 

[Mottie]

Do they have to come from Screwfix? Look here for 1500 and 1700mm rads. https://www.heatandplumb.com/acatalog/central-heating-radiators