Looking for a MicroController Recommedation

I have been mulling a project to emulate MFM disks (DEC RD53 and RD54 in particular) at the disk-to-controller interface. Before anyone asks, I don't want to interface to Qbus (or any other bus) because I want to emulate the least possible hardware and keep my RQDX3 cards working. And yes, I know this has been talked about many times before, but I want to actually start trying this out. My idea is to use some kind of MicroController, talking to specific interfacing logic that drives the lines, and using SD memory for the actual storage. I am considering two approaches: 1. Just record the flux transitions in memory and play them back. This needs me to be able to sample and drive the data lines from the microcontroller at 25ns intervals because the pulse width of the flux transitions is 50ns. This would need a pretty fast microcontroller, but is my preferred solution as it seems the most general. 2. Build custom logic that does the sampling and encodes/decodes the data in 8-bit bytes, so that the microcontroller would only need to read data at a rate of 1 byte every 1.6us. I'd prefer not to do this as it requires me to understand the encoding (not too hard I suppose) and build custom logic, and makes the solution possibly a little less general. I would need a development board that makes it easy to interface to the SD memory on one side and to the custom interfacing logic on the other side (perhaps with a serial interface for debugging too), remembering that there is a 50-pin connector, although only 20 of these are signals, the rest are either reserved or ground. I would need enough onboard memory to store a whole cylinder which is just over 150Kbytes on the RD54. If I am successful I would then like to be able to make several more of the devices, so I would need something that is not too expensive to replicate. I am not sure at this point whether development boards are a good idea for the replication or if I would need to then source the actual microcontroller chips myself and make my own boards. If I have to make my own boards then I would need a microcontroller that is available as a DIP because I am pretty sure surface mounting is going to be beyond me; it would also have to be simple enough for me, who is not an expert in electronic design, to build the other components like the volatile and non-volatile memory, SD interface etc. Looking for recommendations for a suitable microcontroller that does not cost the earth ... Thanks Rob