As Dono pointed out in a comment, this website japanese.stackexchange.com is not a place for questions about translation. I am afraid that you are still confusing meaning and translation.
Usually, さえ is explained to have three meanings (Daijirin, Daijisen):
- It is used to add something on top of other things. Example from Daijisen: 風が吹き出しただけでなく、雨さえ降りだした。
- It is used to state an extreme example to imply that other things are obvious. Example from Daijisen: かな文字さえ読めない。
- It is used in a conditional to signify that the condition is indeed sufficient. Example from Daijirin: お金さえあれば、満足だ。
In translation into English, さえ is translated to many different English expressions, but it is not because さえ has many meanings. It is both because some of these translations have the same meaning in English and because Japanese words do not have one-to-one correspondence to English words.
In your case “君の後ろ姿さえ明日への希望に思えた,” さえ is used to state an extreme example. 君の後ろ姿 is usually a sad thing to see (because it means that the loved person referred to as 君 is leaving), but the speaker considered that even that was a hope for tomorrow, implying that many other things were also a hope for tomorrow.
ように is the continuative form of ようだ, which has many meanings, and in your case, it is used to state a purpose.