Sounds like a reasonable project for the learning experience of digitizing an existing part.

The trigger is definitely a stressed part. You will note that modern lightweight guns with aluminum, scandium, titanium, or even cheap mung metal frames have steel hammers and triggers. Look at the engaging surfaces and think how long they would (not) last in aluminum instead of case hardened steel.

I know of no titanium cylinder that could be adapted. Maybe you can copy the original and use its steel extractor.

It would be interesting to weigh the parts you plan on replacing with lighter material and calculate just how much weight will be saved.