I'd go retro steel hardtail frame, rather than aluminium. Over that distance it'll be a lot comfier, and with a bit of bounce in your tyres you'll be fine. My worry with a retro full suss would be sloppy linkages and a shock that is past its best. A shokpost is a cheap option for a comfy bum, but I've never really got on with them and a decent pair of shorts/liner has always been my friend.
Front forks will give comfort rather than bump soaking ability, but make sure they work. Elastomers are easily replaced, but stanchions can hide a myriad of issues unless pulled out and looked at.
Mid late 90's Kona Lava/Cinder, Marin Bear Valley, GT Karakoram/Timberline and the ubiquitous Orange P7 (because I can't comment on a thread without mentioning them). Can pick them up for decent money and then have some held back for tinkering and replacing anything that needs to be.
Having said not to go full bounce, I've always liked the look of a coilover'd Proflex with Vectors (since Jez Avery rode one in Dirt). Quite a few on ebay for keen money and they still look batsh!t nuts. Simple design and plenty that look like they've not had much use. good few came with Maguras as stock, so that would mitigate any perceived issues with V Bakes (though I've never had any issues) I can think of worse ways to do 50 miles.
