Custom Shimano 12-28

Funkhau53r

Hi

I have a Shimano Ultegra 12-23 cassette and a Shimano 105 11-28 cassette

12-23 goes 12-13-14-spacer-15-spacer-16-spacer-17-spacer-18-(19-21-23)

11-28 goes 11-12-13-14-spacer-15-spacer-17-spacer-19-(21-24-28)

Is it possible to mix and match to arrive at a 12-28?

IE: 12-13-14-spacer-15-spacer-16-spacer-17-spacer-19-(21-24-28)

So swapping out the bottom four sprockets (three of which are on the spider). The top six sprockets would be Ultegra, with the bottom four being 105.

I don't need an 11 sprocket, and ideally would love to keep the 18 to have a closer ratio for the top seven gears.

The cage is good as the bike came with a11-28 cassette, and putting on a new chain to accommodate the extra length between the 23 and 28 is not an issue.

A) Is it possible?
if so, are there likely to be any indexing issues?

Thanks

shadow4532

best guess based on what im running A) yes no

styxd

Yes, I have a mix and matched 28/12 cassette on my bike.