Hello there and welcome.
Cool kit you have there. I'm no Slingerland expert but I'll throw my $0.02 in and see if others agree.
I've seen that type of tom mount before and I think it's more common on single headed kits. Doesn't allow for a wide range of setup options, but does the job.
As for value (if that's what you're looking for) I could be wrong, but I think that the single headed kits are not that desirable, from a collectable point of view. No idea on an actual price, but if a similar Slingy set with double headed toms was worth say $800.00, I'd think that this kit would fetch $500.00 or less.
Again, not an expert - Just my opinion from what I've been seeing in the vintage market. I have no idea what vintage they are as well, but I think the single headed kits were common from the mid 70's till the mid/late 80's.
That said, if you like the way they sound, then by all means clean them up/restore them and use them. As for restoring and selling, even in great shape, I still don't think you'd see big $$$.
I collect and play Kent kits, which are much further down the ladder than Slingerland.
If I'm way of base here, then please, Slingy experts, chime in and correct me. If not, then how did I do? :)