If I can offer a bit of advice as I used to modify my Sharp 12K, Benq W10000 and JVC RS series.
Fabric can easily catch on fire depending on where you put it in the light path.
The lamp would melt/burn a hole in the fabric after a month or so of usage in my case and I did test the fabric (synthetic felt) beforehand for flammability.
Taking zoom lenses apart is a tricky business. I am not familiar with Planar, but the few lenses I have taken apart were all greased up inside so marking the lens is extremely easy.
Ultra steady hands are a must. Cleaning the lens perfectly once smudged is almost impossible and I had a laboratory grade molecular level gel style cleaner...
Sticking anything inside a lens such as fabric is tough as the parts are moving all the time and there is very little room so unless you decide on fixed lens position lining a lens is very tricky.
Most of the DLP machines use shiny metal parts inside optical paths, all the mechanical irises, color wheel chamber etc.
After experimenting with painting the irises black I would say the paint can degrade quite quickly.
I have painted the entire DLP chamber black on my pj, all around the dlp chip and the prism. Based on all the mods I have performed I would say I got the biggest bang for my buck by controlling the light dump zone.
Second best would be painting the iris black. I would leave internals of the lens alone from my personal experience.
There is a special paper for flocking telescopes: "Protostar" flocking paper (http://www.fpi-protostar.com/flock.htm
) that you might want to look into.
It would be interesting to see if you can make the Planar better.
My Benq after all the mods was spectacular and easly the best DLP machine ever created.
However after a month of sleepless nights testing I might have been slightly biased