Looks to be little difference in the price of plain back and D1-3 versions of the 5C collet carrier. Get a D1-3 direct fitting one and if it turns out not so good then buy a backplate and convert the beast. Probably only £20 or so to write off if you do have to convert.
I do wonder how hard it would be to recut the locating taper in a substandard D1-3 mount and adjust the thickness to suit.
If you don't have a stash of 5C collets maybe more cost effective to buy a backplate and switch to ER as the backplate mount holders seem sufficiently cheaper than 5C to more than cover the cost of a collet set.
I'd probably go ER if starting from scratch, spindexer'n all, but my main lathe has a native 5C spindle and I have full sets of both imperial (x 1/64" ) and metric (x 0.5 mm) 5C.
Clive
Edited By Clive Foster on 26/05/2020 16:41:40
Edited By Clive Foster on 26/05/2020 16:42:14
Edited By Clive Foster on 26/05/2020 16:42:33