Hi volks,
It's been a while since I've read the list (been out trying to catch up
with Karl's mileage) so if I'll have been over this already don't read
this ;) I was in All Electronics and saw these batteries. Used 12v 45
amp/hour Yuasa gel cells NPX-150R

It measures   7 3/4" length    6 1/2" wide    6 7/8 tall

The poles are recessed 5/8" (just like the starter battery) and appear
to be 1/4" bolts

Its a non-cataloge item so you'd have to ask for it specifically or go
in and get it. It appears to be a perfect fit. I haven't tried it yet
(figured I'd run it up the flag pole and see if anybody mooned it)
Although its not the Optima (52 Amp/hours) its also not $180.  This
battery appears to be an excellent cheap alternative.
They're url is

http://www.allelectronics.com/

Walter Gomes
86 Westy "Miles"