Lowering and wheel/tyres 1970 GMC

hello, I am about to purchase a 1970 GMC shortbed sidestep. if the inspection of the car is positive, it will be shipped to Holland. the car is completely to my liking, I want to change two things in advance. the car must be lowered and I want to provide the car with different wheels.

Lowering: I was thinking of a 4.5 "or 5" lowering on the front and 7 "on the rear. The car has powersteering and a front power disc brake conversion w / complete front suspension rebuild.Rear brakes rebuilt, new coil springs & shocks front & rear, I don't know if the shock absorbers are suitable for a drop like this or if I need shorter ones I am looking for a suitable complete reduction set I have read this forum for a day or two, but there are quite a lot of different solutions and opinions I want to do a C-notch right away. I understand some dropspindles are better than others.

wheels: I have my eye on the 15 "Black Rock Series 942 Type D Matte Black Wheels. I do not want scrapping tires. I have read a lot about the rim sizes in combination with tire sizes. I understand that on the rear axle 15 inch 10J 4 inch or 4.5 inch Backspacing, with 295-50-R15 tires could fit ? I can't quite figure it out at the front, I read somewhere here that a 4.75 backspacing would be ideal. a 8J is available with a backspacing of 4.5 inches, the 10J is available with a backspacing of 4.5 inches.
I do not want the tires and rims to collide with the inside screens when driving in at maximum or against the wheel suspension. Can I fit 10J all around with 295-50-R15 ore is 8J with 265-50-R15 in the front the way to go ?

I have to ship all parts, so exchanging becomes very complicated.

I found rims on the summit website, if they also have good lowering kit’s, I order everything there. Then it can be sent in one go.

tips and tricks are welcome. I using this car for fun cruising, not on a circuit and not for any kind of racing. In my view the C10/GMC of this age look stunning with the right stance. The roads overhere are reasonable good. I also like the black steel wheels with white letter tyres.

Thanks in advance, the lowering package and wheel/tyre package gives me the opportunity to do it right in once. But the knowledge overhere is pretty limited. I have no unlimited budget to purchase a kit of $5000 and a wheel/tyre package of $5000.

Ron

[PGSigns]

Knowing more about what was used on the truck you are looking at to do the disc brakes would help in determine some of what you need to lower it. Going that amount in the front you can have some issues with 15" steel wheels and the lower control arms with 4" and more of back spacing. The lower you go the more issues you can have with tire and wheel combinations. I always recommend using a wheel/tire fitment tool on the truck you have to see what will really fit your truck with the mods you have. If you are going to buy a complete kit with what you need I would look at Belltech.
Jimmy

[SCOTI]

Originally Posted by PGSigns

Knowing more about what was used on the truck you are looking at to do the disc brakes would help in determine some of what you need to lower it. Going that amount in the front you can have some issues with 15" steel wheels and the lower control arms with 4" and more of back spacing. The lower you go the more issues you can have with tire and wheel combinations. I always recommend using a wheel/tire fitment tool on the truck you have to see what will really fit your truck with the mods you have. If you are going to buy a complete kit with what you need I would look at Belltech.
Jimmy

To add to this info, GMC frequently came w/rear leaf spring suspensions instead of the more common (for 67-72) rear Truck-Arm/coil spring set-up.
You will need to know which it has.