RE: Quique Somenzini YAK-54S 73"
Yes, I'd say that was excessive... About 1" is more like it... yours will be about 2" and look pretty "out there".
An experienced builder would move the firewall back 1". This would entail several steps, not necessarily difficult.
Looking inside the engine box you will see that the Sidewalls of the engine box are two layers with the inside layer being lightened out.
Measure back 1" from the back of the firewall on all 4 corners and draw a line around the inside of the engine box... this is your new location for the back of the firewall.
Draw a line that is even with the lightening holes in the box sides and cut the engine box off flush.
Fill in the ends of the sides with 1/8" aircraft play... a strip of about 1.25" will be sufficient.
A new firewall would need to be made from 2 laminated pieces of 1/8" aircraft plythen glued in place with the back of it meeting the lines you drew earlier.
When set you can glue hardwood tristock (1/4-3/8") to the front and back of both sides of the firewall.
Last, pinn the firewall by drilling about 4 evenly spaced 1/8" hole int he engine box sides into the 1/4" firewall... about 3/4" deep.
Plugged these holes with epoxied 1/8" dowel rods. Sand the dowels flush when set.
This in effect will move your existing firewall back 1" will be as strong or stringer than the existing firewall... and will take only a couple hours at best.
I'm not saying anyone SHOULD do this, but rather that it isn't a hard process if you have the proper tools and are confident in you wood working skills.
This would put the Saito 2.20 hub 1" outside the cowl... just about right...