Replacing fork tubes.

I'm in the middle of replacing my pitted fork tubes with a pair of pattern tubes, couldn't stretch to OEM. The original tubes have a fitting at the bottom which retains the damper rod and rebound spring but the new ones don't.
The fitting appears to be integral to the original tube and doesn't seem to be available as a part, it doesn't appear on the parts fiche.
Am I just missing something or is swapping the tubes a bigger job than I thought ?
Probably serves me right as I only really needed one and one OEM costs the same as two pattern.

tia

If they're ABE then you need to carefully grind the bottom off your old tubes and fit internals in the the new tubes.
DO NOT FIT WITHOUT AS THE THERE IS NOTHING TO STOP THE TUBES COMING OUT OTHER THAN THE SEAL/BUSH

There should be instructions on the bags the tubes are in.

I can get pattern tubes that come with these fitted already.

They came without instructions but they are ABE, though not bought directly from them. I've no garage so have to work outside, last time I looked it was snowing, so I was looking for straightforward replacement and reassembly.
I thought it might involve removing parts from the old tube so I had a poke at it and managed to break the little plastic bit so I'd be looking for a another knackered tube to salvage the part from.
If I can get a tube,or tubes,with inserts already fitted it'll make life a lot easier.I can always save the other tubes for when I've more time/the weather's better or just sell them on ebay.
I'll PM

thanks