Gun Barrel pipe replacement

Hi all, hoping for some clear advice on the issue below. I have a house, half of which was build mid 1980's and fitted with gun barrel piping for the heating. However an extension added on 15 years later, with all the heat piping done with copper. The original rads connected to the gun barrel piping in the older part of the house are now almost full with sludge and emit heat only from the very top part, so it's as good a time as any to pull them and the gun barrel out and replace. The pipes are all buried in concrete floor.

Are there any issues that would pose a problem when doing this work? Anyone undertaken this or similar before? Gun barrel is only in four rooms, so not a huge area. Apart from the older congested rads, heat circulation is generally good. Open vented system with dual fuel (mostly working off solid fuel range but there is also oil boiler outside for nights/periods when away to keep frost away).

Thanks for the advice!

Its just a job of work but you need to clean out the whole system, disconnecting the boiler and stove and flushing them separately