4.460 bore center minus 4.250 bore leaves .210 between bores. Not good unless its already a siamese bore block. Even then its pushing it. Darton offered sleeves for a 6.1 for a while but I know it wasn't 4.250 bore.
Ric3xrt has been doing LS and R5 sleeves in to the BGE and 6.1 blocks since 2016....finally some one else caught on
Dartons 6.1 M.I.D sleeves were designed to go 4.155, which leaves .192 of wall left.
A few years back Ric had one with the Darton mid system, bored to 4.25 , leaves .145 of cylinder wall left , the test mule ran a real short stroke, was between 389-392CI. ran 6.5XX length rods , Idea was to keep the side load down , block had a little bit of hard block to help keep it stiff. I know he's done 2 or 3 with a 4.20 bore and 4.25 stroke, once with a 4.30. and one with a 4.40 winberg crank , the 516ci mule is a billet block with a 4.40 winberg
The Darton LS2/3/7 will work, need to trim the bottom , with the LS sleeve you have more side wall left, .220 if I remember @4.20 bore , I know at his old job they did a few 4.32 bore LS7s with the Darton sleeve and 1 G3 BGE 4.32 bore , paper thin wall , jacket was full of hard block.
