[clowntable]

There's a problem in the concistency of your thinking.
1) You think you have huge implied odds if you hit your FH because he will basically call off his stack
2) You think you can bluff him off the hand
Do you see the problem here?
I doubt he's scared of the flush card if your donk-read is right on the other hand the flush card might have made his flush

I'd say villain should have raised A7, A8, 87 given the board but then again he might just be a station so who knows.
The 6 on the turn is good because now you beat 87 so you're only afraid of the straight that just got there, draws and A7/A8 + sets

I'd say the range is:
Board: 7s Ac 8s 6c
Dead:

equity win tie pots won pots tied
Hand 0: 55.917% 52.86% 03.06% 3256 188.50 { Ah6h }
Hand 1: 44.083% 41.02% 03.06% 2527 188.50 { 88-22, A9s-A2s, T9s, 86s+, 76s, 54s, A9o-A2o, T9o, 86o+, 76o, 54o }

So I might shove turn depending how strong he thinks TP or 2P are. I don't think many villains minraise a spade draw here.

If you call..
River, check behind there should be no hand that doesn't beat you that will call you. I don't know about the FE vs a better two pair (A7/A8) but since he's donkish I doubt it's high.
You should love that you get to check behind here.