Big Tires on 6" Wheels

[dholly]

I'm putting a pair of 21/800x6 Dessers on my 4-1200. I have Matco W62 wheels with wheel covers. All the tubes (for experimental, not certified) seem to have a 90 degree valve stem either too short to go thru cover or too long to cover up. I'd prefer not to put holes in the covers. Anyone know of a source for an appropriately sized tube w/ a straight stem that won't break the bank? thnx

[edit] I called Matco to get the scoop on valve stems for this wheel. The stem exits the face of the wheel which requires a 90 degree stem. Going to try Desser's recommended tube (TR-87 SHORT 90 DEGREE VALVE SKU: TU 700/800-6 GU) and hope the exposed stem is less than 3/4" out. Will report when rec'd.