exactlywhy did you boil some of the pieces? If anything I would suspect that would render some of the fat out of it.
for whatever reason...fats dont freeze dry very well. something about the cellular makeup prevents it from sublimation. i saw a vid where a guy freeze dried a fatty sausage and it just turned to a rubbery inedible mess.
long story made short...there was a place in town years back that bragged about their ham sandwich. it was very tasty and i eventually found out that all they did was boil the ham for a while and then made sandwiches out of it. i got a ham and boiled pieces of it and it did taste better, had a better texture and was less salty. my premise for boiling the SPAM...
on a side note...i have several different rices i use. i happened to use an organic brown sprouted rice for a dish a few days ago and i made extra to freeze dry. that type of rice is hard to reconstitute for whatever reason. some things are just made a certain way where they are not prone to freeze drying.
as for SPAM...we are NOT done yet! i'll slice it thinner and i might skip the pre-freeze on a batch. i will figure out how to make it work for an MRE...