[Tfug] Yet another optics question

[Bexley Hall]

The bulb in the light source for my stereomicroscope is made
of unobtanium-247 (not quite as hard to come by as u-248 but
damn close!).  And, it throws off a *lot* of heat -- 20W!

I am tempted to replace the light source with a set of
white LEDs.  This frees me from the worry of having to
worry about finding another lamp N years hence as well
as cutting down on power consumption, etc.

But, the light source has some optics in it to produce a
focused light:

http://www.science-info.net/docs/b-l/BL_Nicholas_Illuminator.pdf

The "lens" (lens assembly?) appears to be a pair of plano-convex
lenses with a "light pipe" between them (I think this is just to
compensate for the mechanical design of its mount -- but it
may have optical consequences too?).  I.e. the entire lens
assembly is probably 2 inches thick.

My question:  do I need to situate the LEDs at the same position
of the filament in the original bulb?  If so, that would suggest
I need to use a single ultrabright LED as trying to locate multiple
LEDs in the same small region would be problematic.

Or, should I just buy a few bulbs (they are about $10 each), hope
they don't fail prematurely, and just live with all the heat
thrown off, etc.?