[murrelet]

Any tips on how to attach the end of the film to the spool?

I use masking tape: Cut a 1.5 piece of tape, attach about 1/4-1/2" of tape to one side of the film, wrap film + tape around spool, attach other end of tape the the other side of film.

[Xmas]

I use masking tape: Cut a 1.5 piece of tape, attach about 1/4-1/2" of tape to one side of the film, wrap film + tape around spool, attach other end of tape the the other side of film.

Or packaging tape but masking tape is better.

[TomB_tx]

Actually, the genuine Pentax cassettes don’t need tape to secure the film to the spool. Like the Leica, Zeiss, Nikon, Canon, etc. cassettes of the period, the spool has a “capture slot” to hold the end of the film.
You trim the film end so it tapers to a center point (there were trimming templates supplied back then to shape the profile),

insert the point into the slot on the “insert” side (longer slot than the exit side), and the end catches on an internal trap do it won’t pull out.

Then just load the cassette.

When removing the film from the cassette, open it and remove the spool, load the reel, then cut or tear off the end that’s stuck in the spool. Then pull the trapped end out through the opposite side of the spool. (The internal clutch only lets the tongue of the film move one way through the slot.)