...afford a bellows..
Shoot, MAKE a bellows- Freestyle has the fabric, might cost ya $20
Your first try might be UGLY- mine is, but it's light tight.
The next bellows will be better- easier cuz it's not gonna be tapered, for the 7x17 that's maybe half complete [see above].
And did you see that lens Tracy Storer offered for only $500 !!! Convertible, covers 20x24 !!!