That is the same neck (spigot) diameter as the OS 4BK. The best way to get one of these is watch ebay for a ragged out OS 40 or 45 FSR. The OS 4D is very similar, except the neck diameter is .530 instead of .510. These carbs came on the 40 and 46 SF, and can be easily turned down to fit. They are more recent and easier to find than the 4BK. Also, check the Perry web site. They now list all of their carb neck diameters and bores, so you can pick something that will work.

Thanks for the responses. I just ordered a Perry # 4100. It has a 0.340 throat. Conley pretty much choked whenI told him what I wanted it for. But, he gladly took my money.

My goal is to use current production components from normal retail sources unless there simply is no other recourse.

Eric,

Thanks for the word of caution. I figured I was pushing the limit.

Bob