Having so much fun with my 45-70 I thought I might start reloading for it. Have never reloaded for a straight wall case. Any advise as to brands of dies and crimping? Thanks

I use redding dies. I shoot smokeless (RL 7) and do all my 45/70 shooting in a Shiloh Sharps and I never crimp.

I use RCBS dies with Varget and H322 powder and have a mild and a wild load.

I do crimp a little on the mild and a lot on the wild as they are shot through a Marlin 1895 Cowboy and need it for the tubular magazine.

I use Hornady dies for FL sizing and bullet seating. I especially like their bullet seater die, which I use only for seating. The sliding sleeve helps with bullet to case alignment. I use a Lee FCD for crimping. I also have a Lyman neck sizer die.

Rem 405gr. H335. Mag primer. Lee factory crimp die

Is it a single shot or a lever repeater?

Stay away from Lee and Hornady dies.
The Lee seater stinks for short bullets. It will let them tip enough to crush the edge of your expensive cases. The Lee expander die is a total joke and is completely inadequate for cast bullets. Hornady sizing dies with the sliding spindle are a pain to use. I am not sure the sliding sleeve on the seater is made well enough to provide any real precision to the seating operation.
For a 45-70 the expander die is very important.
If you use cast bullets you will probably have to use an after market expander plug such as sold by Track of the Wolf and others. AT least use a Lyman M die or one of the following brands.
I like RCBS and to a lesser degree Redding.
They both have good sizers and seaters.
Redding does make the best seater (the competition seater) by far if you are will to pay for it. The Lee FCD is the best going if you have to crimp. If you are shooting a single shot avoid crimping.

Use loads made up with SR4759 unless you are into capital punishment. IF you have to go fast use IMR3031. There are other powders that work ok.

My 45-70 is stainless Marlin Guide gun.

The 45-70 was originally a single shot rifle cartridge. You probably want to restrict your Marlin to bullets that weigh 405 grains or less unless they are cast bullets specifically deisgned for a repeater rifle or unless you shoot it single shot.

Is your rifle afflicted with a Microgroove bore?

Best bullet i've loaded in the Marlin is the 350gr Hornady. It seems like it gives the best balance between velocity and weight.