Headed to my first race (wish I would have done it when I was younger).
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Question: Hypothetically, if my FTP is 200 (we all know it is much higher right…). How should I plan power output for a 60 mile gravel race.
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The surface is maintained dirt roads and pavement so it is basically a road race, but you do get to eat donuts and erase some time 
Hard to say, other aspects probably come into it but one factor will be your ability to repeat (W’) if its a very punchy ride.
Probably you’ll discover that this is not the most important question! One of the most important artistic skills in mass-start gravel races is picking a group of riders that isn’t going to drop you but also isn’t going to slow you down…and then staying on the wheels. In the initial blast off that most gravel races seem to have it’s important to know (guess?) if this group of riders is going to wreck you or if they are going to settle down & become well behaved right in the range of power you want to be riding. And if they’re not…when to pull the plug and try the next group riding somewhere behind you.
Unless you just want to drift off the back and then ride solo. I’ve done this many times and it’s a great way to enjoy the ride! In that case just start out a little low…say 65%…and then ratchet it up to 75% as your sensations guide you.
I have heard on about every video I have watched is “started too fast.”
So I am determined to keep the start in check.
That can definitely be a fun way to ride a gravel race…because most of the time you’ll end up catching & passing rider after rider after rider.
Just do what you can to stay with a pack of riding that you think are around you ability. It’s much easier to draft than ride solo as if it’s a TT. That said, don’t get dropped by that group and don’t worry about the power to hang on. If you do get dropped, there will be another group behind you that you can jump into when they catch up to you. Rinse and repeat until you get to the finish line. That’s probably the best way to learn
I’d recommend not even looking at your power data. Record it to look at after but that’s it.
Not going out too hard is great advice but other than that just race. Learning to race without looking at data is a great skill. You may even find you can go harder than you think.
FTP is just a number. Zones are just good estimates. How long you can spend in a zone varies by person and can vary day by day.
Race by feel and review the data after. After a few races of recording and analyzing you can get a much better idea of where your power numbers should be and when.
In a road race I’ll never look at power. I won’t even have the field on my computer. For a long gravel race (>60miles) I’ll have it as a field but only as a quick reference. I won’t overthink it.
BWAHAHAHAHAHAHAHAHA!!!
Said every racer ever. 
I would target an IF of around .7 - .75 if this is your first gravel race and then feel free to up the pace in the last 10-15 miles if you still feel good.
Dirty Donut is on my To-Do list, but I am doing FNLD GRVL the next weekend, so it will have to wait for another year. Have a blast….don’t worry too much about power, etc. Just take it all in and enjoy the day.
I know. And I am the worst at holding back. I was at Ragbrai and jumped every pace line that passed me.
130w or less for as much of the 60 miles as possible. A few key sustained moments at 180-200w (less than 10 min). As little time as possible above 200w. And if you’re solo everything you can muster in the last 1-5 miles.
That’s my take on your 200w hypothetical.
In a group: whatever power it takes to follow the right wheel. Solo: tempo.
I 2nd the don’t even bother looking at power.
Particularly, if it’s your first race.
You’ll learn a ton more by just racing on perceived effort. Obviously, record power, but just have a screen that doesn’t display it. Maybe glance at it occasionally. However, going off of some sort of exact IF prescription is light years from ideal.
Race, learn, use data to inform your subsequent races.
Good luck.
I pretty much would say similar to above in that, for your first race you probably don’t want to aim to keep it at, or above a certain wattage, but below a certain number.
For me, I’d be thinking I don’t want to punch too much over FTP if you can get up and over a climb smoothly without. For longer climbs (anything over 10min for example) keep it below 90%. Steady efforts try and keep it smooth and early keep it below 80% on the “free” km’s and start to send it once the doughnuts kick in towards the end.
Go and have fun, it doesn’t matter what your PM says.
Going forward, learn to ride to feel and race tactics.