From the Monroe cattledog:
180B - Type T4, Body length 413, Comp. length 413, Extd. length 599mm.
240K - Type T4, Body length 404, Comp. length 404, Extd. length 687mm.
Just to clarify, the gland nut SHOULD NOT bottom out in the tube.
You need to add a spacer at the tube bottom to bring the strut body shoulder to where the stock insert would sit, e.g. at the same level as the strut tube top.
That will allow the gland nut to clamp down on the top of the insert in a positive fashion.
Do a dry run and mark where the gland nut runs out of thread.
As long as the finished assembly is above the mark you know that the insert is well clamped and won't rattle around inside the tube.
As suggested, oil up the tube.
I leave the oil from the old wet struts in the tube, slip the insert in and let it displace the excess oil, then tighten it all up