i hadnt done this conversion but reading what you have it would seem 5/16 and 3/8 would work just fine 1/2 would be over kill, whats needed it getting 58 psi like you mentioned to the rails.. have you tried the stock lines? the larger of the lines is gonna be a return line or vent line the smaller line would be the feed line to rails or regulator. ( i would think) as for splicing mine are spliced with hose clamps and its been that way almost a year without problems .... sorry couldnt be a big help but i hope ya figure it !!!! good luck