Beautiful!
I like matrix board too - as a kid I did a lot of stuff with it because it was much cheaper than Veroboard, and easier to re-use as well. And, as all my components were "recycled", the short lead lengths were impractical with Veroboard layouts.
I'm intrigued by the negative feedback - did you run into stability issues? I'm just thinking about all the potential phase shifts through the transmitter and demodulator... Also, given that you did it for frequency response reasons, I'm wondering if pre-emphasis might have been easier?
I know very little about RF stuff, so plan to investigate this circuit further - I'm thinking it will be a good project to get my feet wet. The modulation scheme is new to me - every circuit I've seen uses multipliers to achieve AM - did you rule these out on complexity grounds?
BTW, as people are discussing reducing the component count, I reckon you could lose C3, and replace R6, 7, 8 with two resistors. But hardly worth worrying about it - it's not like you're going into production! Personally, I like belt-and-braces design too
All the best,
Mark