[carpdad]

This is a door that leads out to the bulkhead cellar doors, which is not weather stripped. I want to replace existing wood/glass 1 3/8 door with fiberglass (will not rust), but the height is not full door height.
Can I cut fiberglass doors? Is it same as hollow core? If available, I'd just get a slab, cut from the top and keep the bottom weatherstripping/threshold. Thank you in advance.

 

[Windows on Wash]

They have wood blocks in the top any bottom, but I think it would just be easier to order it pre-hung and custom sized.

 

[LanterDan]

I did exactly this about one year ago, only I used a steel door rather than fiberglass (I looked for fiberglass, but had a really hard time finding a flush fiberglass door). In my case I cut it down to about 60" (don't remember the exact measurement). I cut it from the top as you indicate. The center was filled with styrofoam and I used an old chisel to create a channel to replace the wooden block on the top that I cut off. My door was prehung, and disabled and shortened the jambs and reassembled them. I was a little nervous about how it would work, but it all went very straightforwardly.

I looked into ordering one custom sized, and maybe I didn't know the right places to look, but I honestly would have built a door from scratch before paying the prices I was given. I suspect I could have gotten much more reasonable prices if I wanted a door closer to normal height.