How to replace CM fonts with ones compatible with XeTeX (in amsppt.sty)?

Question

I would like to try to patch amsppt.sty AMSTeX style file to make it usable with XeTeX and non-Latin languages (Cyrillic). It looks like i need to replace the following CM fonts or font families with Unicode aware ones : cmcsc10, cmti7, cmr8, cmr6, cmmi8, cmmi6, cmsy8, cmsy6, cmbx8, cmbx6, cmti8, cmsl8, cmtt8, cmcsc10, cmex10, cmex10, cmmibfam, cmmib, cmbsyfam, cmbsy, cmcsc8, cmex8, cmex7.

Whis ones can i use instead, and where can i get them?

Another part of this question is how to use new fonts in amsppt.sty. The lines where the fonts are selected look like this:

\font@\sevenit=cmti7 \relax

Answer 1

I prepared a file amspptfont.tex with the following contents

\chardef\atfontcatcode=\catcode`\@
\catcode`@=11

% the plain fonts
\font@\tenrm="[cmunrm]" at 10pt
\font@\sevenrm="[cmunrm]" at 7pt
\font@\fiverm="[cmunrm]" at 5pt

\font@\tenbf="[cmunbx]" at 10pt
\font@\sevenbf="[cmunbx]" at 7pt
\font@\fivebf="[cmunbx]" at 5pt

\font@\tentt="[cmuntt]" at 10pt

\font@\tensl="[cmunsl]" at 10pt

\font@\tenit="[cmunti]" at 10pt

% the amsppt fonts
\font@\tensmc="[cmunrm]:+smcp" at 10pt \relax
\font@\sevenit="[cmunti]" \relax
\font@\eightrm="[cmunrm]" at 8pt \relax
\font@\sixrm="[cmunrm]" at 6pt \relax
\font@\eightbf="[cmunbx]" at 8pt \relax
\font@\sixbf="[cmunbx]" at 6pt \relax
\font@\eightit="[cmunti]" at 8pt \relax
\font@\eightsl="[cmunsl]" at 8pt \relax
\font@\eighttt="[cmuntt]" at 8pt \relax
\font@\eightsmc="[cmunrm]:+smcp" at 8pt \relax

\catcode`@=\atfontcatcode

Then the following test file

\input amstex
\documentstyle{amsppt}
\input amspptfont

\document

Добро пожаловать в русский Викисловарь — многофункциональный многоязычный словарь и тезаурус, 
в обсуждении и пополнении которого может участвовать каждый.

\proclaim{Proposition 2.5} Let $S_1,\dots,S_m$ be the components
of a $J$-holomorphic cusp-curve $S$ and suppose that each
component $S_i$ is \rom(a multiple covering of\rom) a regular
curve and that Assumption \rom{(1.4a)} is satisfied. \dots
\endproclaim

\define\test#1{%
  {\tt\string#1}{#1 Test of the font}\par
}

\test\tenrm
\test\sevenrm
\test\fiverm

\test\tenbf
\test\sevenbf
\test\fivebf

\test\tentt

\test\tensl

\test\tenit

\test\tensmc
\test\sevenit
\test\eightrm
\test\sixrm
\test\eightbf
\test\sixbf
\test\eightit
\test\eightsl
\test\eighttt
\test\eightsmc

\enddocument

produces the following output

I didn't even try math symbol fonts, which would require very extensive work with Latin Modern Math.