Scaling down to fit 8"x4" loaf pan

A thank you to Nancy and Creamtea for helping me to make this delicious treat!

Do you happen to have muffin tins or custard cups? If so, you can use a couple of them, greased and floured (or lined with cupcake liners) to bake the extra batter. If you don't have muffin tins and want to try to make 3/4 of the recipe, I have sometimes "divided" eggs by beating the last egg slightly and decanting a small amount "by eye". If you don't want to do too much calculating, only adjusting the batter, you could make the full amount of streusel and either use it all or save a portion for another time (or even double it, say, and freeze half for the next time you make this bread). Also, be aware that glass pans bake differently than metal. Some sites say to reduce the baking temp by 25 degrees and check the cake 10 minutes earlier for doneness .

Stan -
Good luck with your baking!
A few suggestions for adjusting your oan size.
My estimate of volume comparison between the 8x4 and 9x5 pans is about 70%, so using 3/4 ingredients might be a bit too much and overflow.
But making either 2/3 or 3/4 will be fussy, with some of the smaller amounts & especially the eggs.
Options - since the original pan capacity is 8 cups, either make the whole batch and cook the extra in a small extra pan, use another 8 cup pan, or maybe just make half recipe in a 4 cup pan (many baking recipes can be halved or doubled successfully).
Or, look at one of the many charts of baking pan volumes (allrecipes, King Arthur Flour, etc) or the article here by Alice Medrich here about making any cske recipe fit your pans.