I tried both of 9legacy's bootstrap and that for 9front, and got
success for both without any patches.

Your method looks difficult to me.☺
1) follow the method by kylejnusbaum@gmail.com
2) put 1.14.1 bootstrap files to /sys/lib/go/go-plan9-amd64-bootstrap,
    and go-plan9-1.15.6 to /sys/lib/go/amd64-1.15.6 (which is written by sl's FAQ)
    set GOROOT_BOOTSTRAP=/sys/lib/go/go-plan9-amd64-bootstrap, 
    GOROOT=/sys/lib/go/amd64-1.15.6,
    GOPAS=$home/Go
then, cd to /sys/lib/go/amd64-1.15.6, and ./make.rc

By the way, I'm looking your opossum source now, which looks like
very compact, because many are hidden under the $home/Go/git.hub etc...
Go is beautiful to me.

Kenji