These are my measurements. 58mm bore and 2.25" hole spacing.
And now that I look back at the link, the hole spacing is off. So I'd need an adapter or to drill out to make it work.
Heres what I would do.
Find the biggest sprocket 40/41/420 that will fit inside the frame, and mount to the hub. It might be smaller then the 43t now.
Buy the 30 series tav
Buy one of those plate adapters. So you can move engine side to side for chain alignment, and front to back for chain tension.
Buy that engine riser, you may not need it, but it would be nice to have jus incase. You can always sell it or send it back.
Buy a 8t and 9t sprocket for tav, jus incase the 8t jumps the chain. Idk, I've never had to use a 8t on a 5/8" shaft.
You will also need 4) 5/16"-24 bolts, 3/4" or maybe 1" to mount the tav backing plate to the engine. The bolts that come with the tav don't fit.
You need 5/16"-24 bolts 1 each 2.5" , 2.75" and 3" long, to bolt the driver to the crankshaft. A 2.5" might be long enough, you jus never know.
Some 3/4" i.d. shims or washers 5 or 6 should be plenty. Use these to line the driver up with driven, it's a must to keep the belt straight as possible.
2 white driver springs. These will help the tav pull the "not so great gear".
The smaller axle sprocket is not idea, but we can tune the tav to help. By installing 1 or both of the white springs, I'm thinkin both. Also can move the driven spring over a notch and help the tav stay in low a little bit longer, allowing the engine to build power before shifting.
It can work, and I think this is the cheapest way to get it going.
See how this works 1st, and if not happy, then change out the 6" driven for a 7" driven and belt to match, I know the 7" will pull better outta the hole, and help the engine get up in rpm, that's all I use.
If not sure, keep asking questions.