Eugen,

Yes, you understand the plans correctly with regard to the BID. You really should have a PDF of the original plans for reference; the OCR version on the Quickheads site is very well done but sometimes the original layout of the information on the page can help with understanding. You can download from my non-curated repository: https://DavidJGall.com/Q/Quickie/Quickie%20Plans/

While you’re building, be sure to notice on page 4-7 the two pieces called “firewall brace” for which the templates are drawn on page 15-2. I cannot find anywhere in the original plans that callout the installation of these parts or their precise location; perhaps it was covered in a QPC but I’m not going searching for it right now. It’s relatively obscure that these are part of the firewall primary structure because the QAC plans left it for the Onan installation chapter (and then never documented it there). I suspect that people who are not installing the original Onan may overlook these pieces. The best reference I can find for these pieces is on page 15 of the Jinx Hawks/Brock McCaman “SuperQuickie Conversion Plans” for installation of a Rotax 503, wherein they refer to these as “existing lower stiffeners.” See the attached picture:

It appears to me that the placement of these “firewall brace” pieces was far enough apart to admit the original steel “pie pan” firewall extension that accommodated the aft part of the Onan engine between the braces, yet as near to the aircraft centerline as possible to leave foot room for rudder pedal movement clearance. These braces were, partly, to stiffen the firewall for the lower, center engine mount from the three-point Onan mounting scheme; the Jinx/Brock modifications put four ply BID pads outboard of these braces to support the new four-point mount for the Rotax. If you’re installing anything other than an Onan I would strongly recommend following the SuperQuickie Conversion Plans for firewall and airframe preparation. You can download them here: https://davidjgall.com/Q/Quickie/

Keep going with the great build progress!

David J. Gall