Would soaking my down pipes in evapo rust clean them

Take them off, clean them and use a rust killer. That will hold it for a while paint it with exhaust paint or BBQ / high heat paint. The paint wears off pretty quickly though.

Maybe wire brush off as much of the loose rust as you can, then treat with phosphorous type of rust cure to get into the pin pricks of corrosion?

HTH

Theres a technique of metal spraying which can be used to build up and repair knackered metal parts - though I doubt its cost effective?

I asked in my local garage if it would be possible to get the exup fabricated into stainless downpipes and he said contact blueflame if anyone needs new ones contact them

Did Blue Flame say they could do it ?

Why don't you ask chad (rcv4) he's an amazing welder, drop him a pm.

I havnt asked them as my downpipe are ok but there'll come a day just passing on what i was told incase anyone need new ones

Get them blasted, then braze all the little holes and potential holes.

Blend the brazing to the contures of the pipes

Get them Powder Coated with High Temp Coating (Avaliable upto 1000 deg)

It's Silicon based