One thing you have to bare in mind is that the audio cable coming out of these old Beograms was double screened. The inner screens carrying the signal return from the cartridge as usual, and the outer screen carrying the earthing for the deck as a whole, the "earth return" being made when plugging into the Beomaster/Beolab.
Some of these Beograms (like my 3000 and some if not all 1000's) had an option of a built in phono stage which plugged in underneath without removing the bottom cover. I don't know if anyone has any kicking around somewhere, but I could do with one if there are any about in working order :)
To cure the hum when using an after-market phono amp is to place a piece of stranded wire into the gap of the Din socket in the adaptor lead (Din socket to two phono's using pins 3 and 5) before pushing the plug into the adaptor's Din socket and connecting this wire to either the amp's earth terminal, or a convenient case screw on the amp. This completely cures the hum problem I found.
I'm not a fan of the stylish "studs" on the platter as a decent support for the record, but you may feel differently. If these could be easily removed and replaced with a felt or wool mat as used by Rega for example, I reckon the sound quality should improve and the record height would be about the same.
Finally, as many of these decks were lightly used, the greases used in lubrication will have solidified long ago, causing the motor to run slowly, if at all, the speed-change and idler support to sieze up and the idler itself to run stiffly. A surprising number of belts were replaced when they weren't initially at fault I found. Swith cleaning lubricant sprays can be got from the likes of maplin and as long as you don't cover the idler, its pulley or the belt with it, you should be able to free the joints and linkages off without too much difficulty. Once this was done on mine and the motor pulley and idler surface cleaned, the deck comes to speed smartly and runs fine from then on (I left it running on "turn" all day to check and all's well.
Good luck!