Gordon's templates are a huge time saver I still use them. At Lowes, I buy a flat piece of 2 x 3' heat A/C duct. If you lay it out right one $10 sheet will be enough. Rather than welding tabs to the 2 x 2 frame I use one 5/16 self tap hex head screw on the left and right side near the engine bay bulkhead. the rest I just use a few nickel size dabs of seam sealer to glue it in place. I fold in the edge about 3/4" on a 45 degree angle to match the engine tin then use a foam Bus H seal to fill in the 1/2 - 5/8" gap. If you need to pull the engine, I just pry the pieces apart with a paint scraper.