Sparhawk... I used the DA Standoffs. The ideal ones will space your thrust plate right at distance that the cowl lines up with very little overlap on the middle former. The only way you will get this measurement is to get your plane and mount the firewall as they differ slightly plane-to-plane based on how you mount your firewall.

I did not want to mess with other standoffs or wood blocks / engine box, etc.. so I used the DA standoffs.. They are too short and that complicated my balance problems.
I should have spaced my engine out another 3/4" that would have been like adding 6 oz to the nose. The more you can get that engine out there the better!

Mount your firewall (with thrust or without) and measure the length from 1/8" in front of cowl to firewall with the cowl taped in place to provide 1/16" coverage of middle former.. subtract the engine length and you have the standoff dimensions.

This is the best way to do it. You can use shim blocks under the DA supplied standoffs like a lot of people do, but if you do you will get a lot more vibration from the engine. I think AG will make a set of standoffs in a day or two.. so why not get custom ones that fit! Wish I had!

I mounted my firewall with zero thrust. I then countersunk the firewall under the right hand standoffs and added washers under the left hand standoffs to achieve the thrust line. I did this as it makes the thrust line adjustable. Putting 3* in the firewall makes it non adjustable and if you are tempted to use washers later to increase / reduce the thrust it can lead to crankcase fractures if not done right... (i.e beveling the standoffs or countersinking the wood)..

Hindsight being what it is however, 3* is just about right so if you can do it accurately, put 3* in from the start!

DP