i think the 11" TLS front brakes do use a different mastercylinder to the 10" SLS brakes as i think they need to move more fluid, best you check the part numbers in the parts book but the servos to the best of my knowledge are the same
i'm not sure i'd go along with fitting the front 10" brakes on the rear axle as i'm pretty certain that will be too powerful for a lightly loaded 88"
there's no real need to fit the shuttle valve in the system, all that is for is a warning light on the dash to indicate if you lose pressure in one circuit but if you want the warning light then fit it by all means
for final clarity i'm guessing you already have a dual circuit servo assisted braking system but only 10" brakes on the front axle, to me all you need to get is the 11" TLS front components and the corresponding mastercylinder
i did things slightly differently when i fitted 11" drums on my front axle, i used 11" rear axle backplates off a salisbury which meant i didn't need to move or change anything, this gave me wider shoes with a bigger braking area and stops me dead, i have a dual line master cylinder and servo under the bonnet and ignored the shuttle valve (didn't fit it) and just plumbed straight to each axle, the front union on the M/C goes to the rear axle and the rear union on the M/C goes to the front axle
11" rear axle slaves are the same size as 10" front slaves
the only thing you'll find by fitting salisbury backplates to a front axle is the slave cylinder won't be a 12 o'clock as the fitting holes are drilled in a different position