Sidestay Sweep
Generally in yachts for rigs without a backstay a sidestay sweep angle of 25 degrees is considered fine. With Dinghies you could perhaps go a bit further forward. Bringing the sweep down to 10 degrees is asking for it unless the sail area is very small.
Compression loads and jibs
Note too that flying a jib adds a huge amount to the compression loads as attempts are made to keep the forestay tight.
Hull integrity
Sidedecks would be recommended or something to stop the sidestay attachment points from bowing the hull in. Foredeck stops forestay from deflecting the hull. Mast step needs to cover a bit of area and you have to be sure that the bottom won't be pushed off the hull - maybe tie the mast step into the front bulkhead with a couple of ply gussets glued to either side of the step - need only be a 3/16" ply as a minimum - if they ran up the bulkhead 8 inches and were attached with some 3/4square cleats it would be enough.
Spreaders
Boats the size of the PDR rarely use spreaders - the masts are usually so short that buckling is not an issue unless the mast is seriously underspecified.
Usually the spreader is set up in small boats to deflect the stay outwards by about an inch and pull it forward somewhere between half and a full inch. Setup of spreaders is a very critical process in raceboats with probably about 30 to 50% of tuning time devoted to getting them right.
Use of a mast partner with a keel stepped mast
There are advantages if a conventional boom is being used to having the mast step in the bottom of the boat but also prevented from moving forwards or sideways at deck level by a simple open backed partner that runs off the foredeck. It prevents the mast bending forward or sideways excessively particularly under the load of the boom vang and allows a lighter mast section to be used.
Note that usually the mast needs to be protected from denting in the partner area - usually this is done by cutting a section of the mast material and making a plate that covers the area at the partners. in effect a plate over the front and sides of the mast - it doesn't need to be very big (4" or 100mm is plenty). With wooden masts I would either use a bit of aluminium as just suggested or put 3 or 4 layers of fibreglass around the mast at partner level.
More on boom vangs
Many people who move to conventional stayed rigs will be thinking of using a conventional boom.
If using a conventional boom a boom vang is critical to the performance of the boat. It stops the boom from rising and so maximises the amount of sail area projected to the wind by reducing sail twist. It is the single most important sail control and would add around 10% to 30% to the speed of the boat downwind compared to a similarly rigged boat that doesn't have one. Sprit rigs and Balance Lug rigs don't need vangs. Everything else would get great benefit from controlling the twist of the sail
The mechanical advantage needs to be an absolute minimum of 3:1 and around 8:1 is much better. Use low stretch ropes. 8:1 can be achieved with three blocks (pulleys) using a cascade system.
Don't use a yoke (forked end on the boom that engages the mast) if using a decent vang system - it operates through a different rotational centre relative the mast axis ensuring that fittings will be ripped out the mast or boom somewhere.
Cascade system is:
It is possible just to tie up a vang between the mast and boom with some decent low stretch rope. But there are quite big benefits to be had from making the vang adjustable.
Dead end of vang rope is attached to mast base. - it goes up to the boom (a minimum of 2ft back from the boom front. It passes through a block at that point. Immediately after passing through the block on the boom it is cut and a block is tied to the end of the rope with a bowline knot.
A second rope is tied to the mast base. It goes up and passes through the block tied in the end of the first rope. It then can be tied back to the mast base with a trucker's hitch. This is a theoretical 12:1 system but frictional losses probably make it more equivalent to an 8:1.