@DannyP - You (and maybe some others) might be interested in the throttle adjustment tool I made. It attaches to a longer case stud near the distributor/fuel pump block-off plate and uses a CB Perf hex bar throttle lever to move both throttles, equally. It doesn't care what the engine is or whether sitting mid or rear.
https://www.cbperformance.com/product-p/3403.htm
Photos below:
Here's the tool - There isn't much to it. The throttle lever costs under $15 from CB Perf and I modified it with angle grinder (and went overboard in one spot) to allow it to slip onto the hex bar more or less in the middle. I drilled and tapped for another set screw against a side flat of the bar (the new screw is lined up with the short end of the Allen wrench in the photo). I got the knob at ACE Hardware and it screws onto the rod, which is threaded for 10-32 at the knob end, and bent into a loop at the case end to slip onto the stud.
Here it is installed on the engine. You can see the new set screw - It attaches in well under a minute. Simply turn the knob down to increase throttle - It takes only a turn or two to get up to 2 Grand RPM on the engine. The adjustment rod goes through a barrel fitting (same as on a lawnmower throttle cable - also Ace Hardware) that is just there to guide the rod and keep it from binding. The bottom of the knob pushes against the top edge of the lever - really simple. There is a thrust washer under the knob against the lever - just because.
And here's the bottom end of the rod attached to the engine case stud. It's pretty easy to double-nut the stud, remove it and install a longer one in it's place if what you have isn't long enough - Locktite Blue the new stud going in. You could also flatten the rod loop a bit to make it thinner, if necessary, but most case studs stick out a bit, anyway. If you made the rod loop tight to just fit an 8mm stud you just have to anchor it gently for everything to be stable.
Once it's installed, just turn the knob down to advance both throttles equally, just like the cable pulling on its' lever. You can slowly advance it while watching the tach to get to 2 grand and then it holds it right there for as long as you want (or if your shoes begin to melt while standing in the hot air from the heads). It'll hold securely from idle to WOT and once set, the rpms stay put - also perfect for setting total advance timing at 3,000 rpm, no? It also makes starting the engine a bit easier as you can give it a 1/2 turn, just start it up and then adjust the speed.
This was the third time I've used this tool and I've been impressed with how well it works both times. Easy to make, easy to use and stable as a rock.