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[does not allow two stroke timing kit to be installed on Yamaha RD two stroke twins when the engine is in the frame]

Unfortunately the Ebay listing says "(WILL NOT CLEAR COOLING FINS OF AIR-COOLED HEADS)"  It would be cool if you could purchase the machined base with a longer housing by itself to use with a small face dial gauge.

You can get just that from Motion Pro. Just search adapter kit for aircooled engine

Good find. It's only ~$13 and it has a set screw to capture the indicator.
https://www.motionpro.com/product/08-0249

One problem though:  Adapter kit does not allow two stroke timing kit to be installed on Yamaha RD two stroke twins when the engine is in the frame. Adapter kit with two stroke timing kit does work with engine out of frame.

I just cut a piece off the top to make it a bit shorter and made a new set screw hole, so that I could use it with the motor in the frame

Unfortunately the Ebay listing says "(WILL NOT CLEAR COOLING FINS OF AIR-COOLED HEADS)"  It would be cool if you could purchase the machined base with a longer housing by itself to use with a small face dial gauge.
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You can get just that from Motion Pro. Just search adapter kit for aircooled engine

Found this on Craigslist.
Description says its a RD250, but looks like an R5

https://vancouver.craigslist.org/rds/mpo/d/surrey-rd-250-engine/6870487721.html

Its been a long time since I made my own pipe from A graham bells book, but if I remember correct the stinger diameter was based on a percentage of the inlet pipe and the length 12 times the diameter. 

Can somebody explain how the stinger lengths work in GP pipes (both silencers on same side)
The outer pipe has a much shorter stinger than the inside pipe.
I can find a lot of info on stinger diameter and length, but not on using two different lengths together