From my experience when linking games they both need to be running the same software revision. Off Road Challenge is on Midway's V Unit hardware. (same as Cruis'n USA and World) and does not have a hard drive.
With that said it will require burning some new EEPROMS. The MAWS database would be pretty helpful determining which specific rom(s) to burn by comparing the two versions. That has been down for what feels like ages at this point and I begin to wonder if it's ever coming back.
With all that being said I took a look for you and it looks like you could upgrade your 1.40 to 1.50 by having U10,U11,U12 and U13 burnt from the offroadc5 romset.
Differences between 1.40 and 1.50
<rom name="orc-1_5.u10" size="1048576" crc="f464be4f" sha1="da6c04ae49d033f92cdd62f997841365c4a08616" region="user1" offset="0"/>
<rom name="orc-1_5.u11" size="1048576" crc="eaddc9ac" sha1="a6b810bf7460e3257bf6acdc3b79c532fb71ad68" region="user1" offset="1"/>
<rom name="orc-1_5.u12" size="1048576" crc="a2da68da" sha1="b8dcc042b9926055bff9020599c1c218f08b1727" region="user1" offset="2"/>
<rom name="orc-1_5.u13" size="1048576" crc="b4755ee2" sha1="1c4cde7ca60a6e8bff12aed348e7148e20a8caba" region="user1" offset="3"/>