No need. I just submitted a changeset which both fixes the timing issues you mentioned, and gets 300-baud tape loading working.

Updated single-driver build: http://polygonal-moogle.com/mame/astrocade/astro64_190318.zip

Random screenshots:

[Linked Image from i.imgur.com]

[Linked Image from i.imgur.com]

[Linked Image from i.imgur.com]

[Linked Image from i.imgur.com]