I'm with Don here, I would definitely at least consider skipping Ambassador here.
Feodum here is viable, and I think it can definitely beat Advisor BM, and it can also probably beat the engine. The engine payload here is, I guess, double Province buys with Messenger as +Buy, 7 Silver (Silver is better than Gold here), and as many Advisors as you can grab. You have two options to thin: Ambassador gets you really thin, and Trade replaces opening cards with the payload of your engine. Trade does really well here actually, but without Feodum it would pretty clearly be best to Ambassador away all your junk. Advisor makes it hard to actually draw your Ambassador though, and you never have to draw Trade... But I would still do Ambassador without Feodum.
But the Feodum slog here is really good! You can use those same Messenger and Advisor for support, and all of the junk Ambassador hands you is just fuel for Trade, which gets you two silver and two fewer junk for $5. Once you trash a few Copper and Estates, even a single Advisor in hand will help your turns (plus it it's the junk you want to get rid of into your hand for you earlier anyway). Ambassador attacks just become Trader fuel for you. You can then buy Feodums while your opponents deck chokes on Provinces. If you need a quick points injection, you can trash 1 or maybe 2 Feodum for a bunch of Silvers with Trade.
So basically I think Feodum beats BM and engine here because you can let the opponent choke on green (Advisor as only draw is a big drawback) and the game will drag on long enough for Feodum to be worth points eventually.