I just did a full sound system update to our 7050 this summer. Pioneer deck plus 5 1/4" front speakers! 
The full size decks fit just fine once the mounting hole is cut out but it will need to offset up just a bit though so the bottom of the deck lays where the bottom the original face sat. I cut out the old speaker holes to fit 5 1/4" speakers as well and could have went larger and fit 5 x 7's too. I haven't got around to it yet but I plan to add pair of boxed 6"s or 8"s behind the seat some day so I pulled the wires for them down when everything was apart.
Two things need to be done to add newer digital deck though. One is you will need to pull a 12 volt live wire in from the battery being there is no decent constant live wire up there to tie into that can support the power requirements the new decks take and second, more than likely the old foam cab heat and AC liner up there is junk too so plan to replace that as well.
I just put a new piece of 1 1/2" foam in that covered the whole roof cavity which greatly improved the blower airflow and noise plus made a substantial improvement in the speaker sound quality being the speakers were no longer mounted in an acoustically undampened metal box plus it added ceiling sound dampening and thermal insulation as well.
As for getting wiring up there, the main cab frame has is open from the roof down to just above the rear axle on the left so pulling a live power wire and optional rear speaker lines through that is dead easy too. I tied into the main battery power with a 20 amp circuit breaker on the new live line.
Lsst, while you're up there go nuts with the air hose and clean your heat and AC cores along with everything else out. Ours could have grown potatoes in the dirt up there. 
Also if you do much night work while you're at it it would easy to add an extra power lead going up to the roof that could run some cab mounted lights off a relay that is activated by the main lighting circuit as well being those two little light on the front half way up the sides of the cab are darn near useless by themselves.
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