Work on nginx and spdy is always ongoing so there bound to be changes between 1.6 and 1.7, see http://hg.nginx.org/nginx/log?rev=spdy
spdy comes down to a few files;
src\http\ngx_http_spdy.c
src\http\ngx_http_spdy.h
src\http\ngx_http_spdy_filter_module.c
src\http\ngx_http_spdy_module.c
src\http\ngx_http_spdy_module.h
You might be able to simply take only spdy from the 1.7 version if you don't want all of 1.7
spdy comes down to a few files;
src\http\ngx_http_spdy.c
src\http\ngx_http_spdy.h
src\http\ngx_http_spdy_filter_module.c
src\http\ngx_http_spdy_module.c
src\http\ngx_http_spdy_module.h
You might be able to simply take only spdy from the 1.7 version if you don't want all of 1.7