Thanks for sharing (the infor on the modular BITX boards). I actually had a similar idea a number of years ago and designed a small PCB for the ubiquitous BITX amplifier design. I have the project shared on OSH Park and you can get three of them shipped for $5.
The project is shared here.
73,
Ryan AG4ZP
https://oshpark.com/shared_projects/6mnfQQ6e
Another Source for BITX Amp Boards – AG4ZP

If someone wants an SMD TIA for experimenting, I have the boards shared here: SMD TIA
Nice work. Incidentally last year i tried a double sided,child card (smd) that parks 2TIA units , one on either side. it could be plugged to main board by 5 pin connector (Gnd, In,out, Vtx, Vrx) I would love to share the eagle artwork. I could not fine a way. Please enable me send them to soldersmoke. regards sarma vu3zmv
Sarma: If you could somehow send me the file, I could put it on the SolderSmoke server for download by others. send to: soldersmoke@yahoo.com Thanks, and 73 Bill