This seems to be a CTC model. CTC is not really the best option for a good end-to-end system. Encoder-decoder-attention models or RNN-T models are both better alternatives. There is also not really a problem about available open source code. There are countless of open source projects which already have that mostly ready to use, for all the common DL frameworks, like TF, PyTorch, Jax, MXNet, whatever. For anyone with…
I question that you need full attention in the acoustic model. The pronunciation of a word in the middle of phrase does not have much dependence on the beginning. You do need attention in the language model part of the pipeline
See for example here as an overview (my own work, already a bit outdated, but attention has even improved much more since then): https://openreview.net/pdf?id=S1gp9v_jsm