motor and trans swap

Hi, I have a 58 chevy apache. I have purchased a 1967 pontiac 283 and a 4 speed out of a 74 camaro. I am going to be dropping them into my truck and was wondering if there is going to be any issuse with mounting points and also what type of engine mount would you recommed. This truck came stock with a 235 and a 3 speed manual.  

Mounting will be interesting, at best.

The 235/3-speed used a front engine mount, and behhousing mounts, for the tranny.

The Camaro combo should have been a side mount motor, and tailshaft mounted tranny.

Crossmember kits shouldn't be too hard to find, but placement is critical, to avoid issue with the original crossmember.  It needs to stay, as it supports the frame at the rear spring hangers.  
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1949 Chevy 1 1/2ton, home-built hydraulic wrecker.  Rustoleum industrial black, with flames.  Flamethrowers out 5" dual stacks.
1962 Chevy C-20, 402BB, 4-speed, 3.90 positrack. Hauls my camper.... among other things.
Kaiser M35A Deuce, 4x4 4 wheel steering *work in progress*

I expect yer motor has bosses in the front of it for the original type motor mounts,allthou I seem to recall they are slightly different from I-6 to V-8.
the real problem is you have the wrong bellhousing, and using 'stock' motor mounts with an aftermarket trans crossmember will overstress your current bellhousing.
You'd prolly do best to buy both engine and transmission crossmembers, aftermarket.