harleyKmodel

Does anyone manufacture DC Linkert float bowl extensions? I'm looking for one new or used, Thanks in advance!

Do you know this website: http://www.linkertcarbs.com/ They may be able to help.

They are easy to make and you will also want the factory recommended carb spacer. If you have a competent agreeable machinist the carbs are easily converted to DC11 specs.

What bike or bikes do you believe the DC 11 was stock on?

Wasn't really "srock" on any bike. The race department (and others) made some mods to a stock DC and decided to stamp them DC-11.

There are only small differences between any of the DC series and simple jet changes and mods can be done on any of them.

You can still pick up NOS bodies and stamp any number on there you like.

DC-11 Linkerts were delivered on all Sportster XLRTTs from 1959 (part # 27155-59R with 29013-58R back plate assembly) until the advent of the Tillotson race model HD5A in 1967.
The last Sportster XLRTTs in 1971 get Tillotson HD43As.
The DC11s are listed on all the race department motor test cards of the individual Sportster XLRTTs built before the Tillotson race model introduction in 1967.
According to former Harley Race Department members the DC11 carbs were built at Linkert to Harley's order just like the previous MR3, MR4, and MR4A and stamped DC-11 in the same font as the other DC Linkerts.
Ferrous_Head if you have any published or internal Harley Davidson documentation to the contrary please share. (not the stuff on the guy who rebuilds carbs website)
Could there be carbs available represented as DC11s that are not DC11s? Of course. As in all purchases "buyer be aware".
The most expeditious choice would be a 38mm round slide Mikuni which the Factory Racing Department would have used had they been available.