how to determin if I can remove a monoflo system

Hilly

Basically where should I start?  I love heating and reading on it (plumbing by trade) but I rarely get to put it to practice so most of the time I just sit around here reading, listening, learning.



I have a monflo system that has a 1.5" truck that leaves the boiler for 20'.

It goes down to 4 3/4" lines, 2 go north and 2 south and then cover the perimeter of the house.  1 of each feeds heaters on the main floor and 1 of each feeds heaters on the 2nd floor.  when they loop back to the boiler each set tees together and pipes through a zone valve for control (one for each floor totaling 2).  The whole point of the job is maximum headroom in the basement.  If I raise the 3/4" lines in the joist bays the monoflo tees will be on their sides with the branches lying parallel to the floor.  Should they always be graded upward or downward in the direction of the risers?  What's the easiest way to determine if the 1.5" line is a requiorement.  I'm going to assume that one upon a time there was a castiron boiler with a single pipe monoflo doing one loop around the basement.  I'd guess that it was cut back to 20' whenever the electric boiler was install and at the same time they put in the split monoflo loop and added the zone valves.



HTU's are 9"BB cast rads and 4 20"H section rads all piped with 1/2" risers.  I have access to all the risers in the basement still and the home owner (rental property) wants to maintain just 2 zones.  Could I just setup a primary loop (acceptabel practice on an electric boiler??) and then have two manifolds that have all the heaters home ran in 1/2 hePex?  Each manifold could be zoned with a circulator or zone valve.



What's my best way 'out of' this one'? 

If I decided to manifold, where should I start with determining the sizes?  I know heat loss with probably be the first proposed idea, but I know the owner will not be interested in adding or removing any HTU's.  He claims it works and wants to just clear up the pipes in the basement.  Could I take the current BTU output of the current heaters and base my pipe sizes on that? 



Also he wants all the copper taken out and put back new or replaced with pex.  I'm not overly interested in soldering up a dozen or more monoflo tees with pex fittings.  I feel like the cost of the manifolds and that type of install would bring down the labour cost and it'd be a bit nicer of a system in the end.  Any thoughts or comments are appreciatively accepted.  And if you made it this far thank you very much for reading through my mess. Ha