V-Belts with Lycoming standard pulley dimensions

I have this belt today, a Bosch 1170FXST 9.5x850 La

I tried to Google the type but I cant really find any suitable substitute with the metric definitions of today. Talked with a guy that worked selling V-belts end he directed me towards the XPZ850p type.

Do you have any suggestions of where to find a good v-belt for this application?

I would like it to be a little bit shorter because the pulley on the alternator sits really close to the cowling today.

Here are some options - 850mm is about 33.5 inches.

https://www.rockauto.com/en/tools/b...lt,+++++++++++++3/8"+++++(9.5mm)+belt,1000578

Another option is to use one of these link belts - "power twist" - and play with it to get the right length.

https://www.amazon.com/V-Belt-8-Inch-Adjustable-Perfect-Woodworking/dp/B08GYZBLGL/

I like the source . . .

https://www.gates.com/us/en/power-t...motive-v-belts.html?fl-topwidthmm_double=10.0

Here is the Gates XL type I use and came with my alternator. It shows an 851mm and jumps to 838mm length this will bring your center to center distance ~6.5mm closer if you have the adjustment room. You might buy both and install for a baseline check. The 9.5mm width (you have) will spread the centers so the 851mm (#7335XL) is likely your best fit.

The site offers the part numbers so you can source them. The XL series is appropriate for the alternator. I use a 7355XL and is also 10mm width, thus confirming that for you.

It is important to source a proper belt as there are a million different v-belts with different grip, thermal expansion, reinforcement and vee dimensions. Most v-belts shrink as they increase in temperature to reduce slippage.