Hi Stampman! That is a very interesting looking stamp. The way I see it, it looks like the right outer line is really curvy and quite close at top. I also see the top outer line as being high over the 'AG', and then dives to the right. looking on
www.stampplating.com, I went through all the plate 2L photos and only one really matches very closely - 88R2l. That database also says there is a guide dot at LR, which is faint, at best, there, and I cannot see it on your stamp. Looks like it might be covered by the cancel. Anyway, that's my guess.