Now on the other hand if you want to try using the existing TRS-80 analog board and matching CRT, and getting a Mac logic board to drive it ... that might just barely be possible, maybe.  It's been established around here before that the timing and resolution of compact Macs is close to EGA, and needs just a simple level and sync converter circuit to drive some EGA monitors. 
 

johnklos said:

compact Macs put out 22.3 kHz, if I remember correctly. EGA is 21.8 kHz, which is close enough that it should work

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If the TRS scans at a similar rate, and has a similar number of lines of vertical resolution (342 lines for the mac), and the same page refresh rate (60Hz) you might be in with a shot.  It won't be plug and play by any means, but it would mark it out as possible, with some signal adaption.

Here's a thread that discusses some of the complexities and gotchas.