If your end-fed is a random length it should be OK with the mast - you could actually use it as a sloper if it’s too long to just come down the mast (or you could fold the excess back on itself at the far end). If you have a specifically tuned end-fed for a particular band then you may have issues with the reduced length of the mast.
You also need to think how you will support the mast - are you going to have some form of base spike and guy ropes and pegs? Do you know if there is anywhere your can strap the mast to for support on the summits you are going to? If so take some cord or short “bungies” to do this with.
UPDATE: I presume you are wanting to operate on 40m & 20m - if you only need 20m and up -this antenna, (a linked end-fed) from Lambdahalbe is designed for use with a 6m mast.
I used a SOTABeam quadbander 80/40/30/20m with a Decathalon 6m travel mast last weekend with good effect. Richard from SOTABeams also does 3 and 2 band dipoles that don’t take so much horizontal area if required.
There are some photos on my reflector report. I’m a big fan of resonant antennas.
My go to antenna is a trapped 40/20 dipole with a 6 metre mast ( sotabeams 10 metre with 2 largest section / 5-6 smallest gone). I also use a 20 metre dipole on a 4 metre mast for barren summits. All in the Canadian Rockies.
thanks! i really use this design a lot on small or crowded summits. it is quick to deploy, you do not even need to leave your operating position, and it is fairly effective. currently, I combine it with a T1 tuner in order to compensate for ground variation and sloppy deployment; this is much faster than tuning the antenna on site. the next version will include an l-match tuner directly in the winder, but I am currently busy with activations, so it will be a winter project.
My “standard” kit is a pole that gives me a maximum height of 6m, I usually use a doublet with a leg length of approx. 17m as an inverted “V” and an ATU for all bands 80m and above. In very windy conditions I have only deployed the upper sections of the pole to give an apex height as low as 3m with acceptable performance. In very wet conditions to save deploying the ATU I’ve used single band resonant antennas with equal success.
Many thanks for your ideas. They inspired me and although I ended up with using the old good LNR 40-20-10 (I could not make anything else due to time constraints just before departing to the mountains), I definitely will use some of the presented solutions to test early next year.